Radiometer

Handbook

Proper sampling techniques and tips on how to avoid preanalytical errors in blood gas testing.

Troubleshooting

Exceptionally high or low values of a given parameter may be due to a preanalytical error.

Skill test

Test your skills on avoiding preanalytical errors in blood gas testing.

Blood gas Preanalytics app now available

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Studies show that preanalytical errors are the reason for 62% of all errors in laboratory medicine [1]. "The diagnostic consequences depend on the magnitude of the preanalytical error. In worst case, these errors may lead to mistreatment of patients; in all cases, these errors are an extra workload for the hospital staff involved" [2].

This app focuses on the preanalytical phase of blood gas testing and what operators can do to avoid errors. The recommendations are based on existing literature and international best practices.

Examples are constructed, unless specific reference is given, with the purpose of illustrating the consequence of preanalytical errors.

The content provided here is owned and maintained by Radiometer Medical ApS, a Danish limited liability company with its registered office at Åkandevej 21, 2700 Brønshøj, Denmark ("Radiometer"). For more information on Radiometer, go to www.radiometer.com.

References

Disclaimer

Radiometer is furnishing this item "as is". Radiometer does not provide any warranty of the item whatsoever, whether express, implied, or statutory, including, but not limited to, any warranty of merchantability or fitness for a particular purpose or any warranty that the contents of the item will be error-free.

In no respect shall Radiometer incur any liability for any damages, including, but not limited to, direct, indirect, special, or consequential damages arising out of, resulting from, or any way connected to the use of the item, whether or not based upon warranty, contract, tort, or otherwise; whether or not injury was sustained by persons or property or otherwise; and whether or not loss was sustained from, or arose out of, the results of, the item, or any services that may be provided by Radiometer.

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Handbook

In the handbook section of this site, you will learn more about proper sampling techniques for arterial puncture, arterial line and capillary sampling and get tips on how to avoid preanalytical errors in blood gas testing.

To begin, select the type of blood gas testing you are interested in learning more about from the menu on the left.

Sampling techniques

Illustration

The purpose of an arterial puncture is to obtain an arterial blood gas.

The recommendations shown here are based on best practices and international guidelines. Be sure to follow local procedures.

Preparing for an arterial puncture

Make sure to have all necessary utensils ready before entering the patient room.

Mail me the checklist

Performing an arterial puncture

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Sampling device

Illustration

Selecting the right sampling device for arterial punctures can help reduce the risk of preanalytical errors in blood gas testing.

Therefore, when selecting a device:

  • Use self-filling syringes: they fill readily when puncturing an artery and, consequently, a lower fill rate indicates unintended puncture of a vein.
  • Choose short-beveled needles: they are easier to position inside the artery and reduce the risk of puncturing the opposite artery wall.
  • Select preheparinized syringes with a sufficiently high concentration of heparin to reduce the risk of clots.
  • Use blood gas syringes preheparinized with dry electrolyte-balanced heparin to reduce the risk of electrolyte bias and sample dilution.
  • Opt for prebarcoded syringes to reduce the risk of patient-sample mix-ups.
  • Choose syringes that come with a tip cap that is vented to ensure the safe removal of air bubbles and to avoid contact with patient blood.
  • Use automatic mixing of samples to ensure sample integrity.

Operator safety

Illustration

Needle-stick injury and unwanted contact with patient blood are daily risks for operators collecting blood gas samples.

This can be caused by

  • Unavailability of sampling safety devices for operators
  • Lack of a dedicated procedure for operator safety
  • Dedicated procedures for operator safety are not followed

This can lead to

  • Operator concern over own safety
  • Needle-stick injury
  • Infection by blood-borne pathogens

To avoid risks

  • If available, use a safety device that limits the risk of contact with patient blood, e.g. a tip cap
  • If available, use a protection device for the safe removal of needles
  • Ensure a dedicated procedure for operator safety is established and followed in your facility

Patient & sample ID

Incorrect or missing patient and sample IDs are some of the most frequent - and critical - preanalytical errors occurring in blood gas testing [1].

Errors can be caused by

  • Lack of patient identification and/or sample labeling
  • Transcription errors due to manual data entry
  • Lack of a dedicated procedure for identifying patient and samples

Errors can lead to

  • Noncompliance with local and national regulatory requirements
  • Misdiagnosis of a patient’s condition
  • Incorrect treatment of a patient
  • Need for resampling, which is both costly and time-consuming
  • Lost billing opportunities from tests that cannot be accounted for

To avoid errors

  • Use at least two patient identifiers when collecting arterial samples [2], e.g. patient’s name and date of birth or an accession number
  • Make sure the arterial syringe has a patient ID label attached to it before you leave the patient
  • Use a prebarcoded arterial syringe, if available
  • Always enter a patient ID into the analyzer before analysis
  • Use barcode readers whenever available – both for bedside identification and at the analyzer – to avoid transcription errors

Attach the barcode label vertically on the syringe as shown below.

Illustration

References

Sample contamination

When doing arterial punctures, there is a risk of accidentally puncturing a vein. Even a few drops of venous blood mixed with the arterial sample can cause bias on the patient results.

Example

Two samples are collected by arterial puncture. One is accidentally contaminated with a few drops of venous blood before the needle is correctly positioned in the artery. See below how this can affect patient results.

Table

Venous blood in an arterial sample can lead to

  • Bias on O2- and CO2-related parameters

To avoid errors

  • Use self-filling syringes with dry electrolyte-balanced heparin: they fill readily when puncturing an artery, consequently indicating that a vein has not been damaged
  • Use short-beveled needles: they are easier to position inside the artery and reduce the risk of puncturing the opposite artery wall
  • Make the puncture at an angle of 45° for better positioning [1]

Illustration

Read more

References

Heparin-induced bias

Illustration

The use of non-compensated heparin in blood gas syringes can cause a bias on electrolytes and metabolites, which ultimately may impact patient treatment [1]. The bias on the electrolytes and metabolites will likely be unidentified and variable; however, it can be avoided.

Heparin is the only anticoagulant that is recommended for blood gas analysis [2]. The use of heparin as an anticoagulant is needed to reduce the clotting of the blood gas sample. Clots in the sample may interfere with the analyzer and produce inaccurate values [3].

Bias on electrolytes may be caused by

  • Heparin that is not formulated to reduce bias on electrolytes
  • The use of liquid heparin

Formulation of heparin:

Heparin binds to positive ions. This effect has most impact on the concentration of ionized calcium in blood: The higher the heparin concentration, the more pronounced the bias. IFCC states that if heparin concentrations above 15 IU/mL are needed, heparin should be formulated to compensate for the bias on electrolytes [4]. This special heparin formulation, which does not cause bias on electrolytes, is called compensated or electrolyte-balanced. Using electrolyte-balanced heparin allows the usage of a higher concentration of heparin to reduce the likelihood of clotting .

Liquid heparin:

Heparin can be formulated both as a dry heparin and as liquid heparin. Use of liquid heparin will inevitably, in contrast to the use of dry heparin, lead to dilution of the blood gas sample and impact electrolyte and metabolite values.

The dilution effect will vary from sample to sample, depending on the volume of liquid heparin versus the volume of the blood gas sample.

If the volume of liquid heparin is 0.05 mL and 1 mL whole blood is sampled (Hct 45 %) it will dilute the plasma phase by approx. 10 %. Since the electrolytes and metabolites are measured in plasma, the concentrations of these parameters will decrease accordingly.

Examples of heparin-induced bias

Due to the formulation of heparin:

  1. Non-compensated heparin may cause an error on cCa2+ of as much as 6 %. This means that a sample with a true cCa2+ of 1.15 mmol/L (4.6 mg/dL) will report a value that is 0.07 mmol/L (0.28 mg/dL)too low – that corresponds to 50% of the reference range (1.15-1.29 mmol/L (4.6-5.2 mg/dL)) [1].
  2. A non-compensated heparin concentration of 15 IU/mL blood, for example, causes an approximate 0.03 mmol/L (0.12 mg/dL) reduction in ionized calcium. This negative bias rises to 0.15 mmol/L (0.6 mg/dL) with a heparin concentration of 50 IU/mL and to 0.19 mmol/L (0.76 mg/dL) if the heparin concentration is 100 IU/mL [5, 6]. The typical reference range for ionized calcium is 1.15-1.29 mmol/L (4.6-5.2 mg/dL).

Due to liquid heparin:

  1. If the dilution of the sample with liquid heparin is of approximately 10%, true glucose of 5 mmol/L will be measured and yet be reported to be 4.5 mmol/L (81 mg/dL). The same applies to sodium: true sodium of 140 mmol/L will be measured and yet, due to the dilution caused by the use of liquid heparin, be reported to be 126 mmol/L.

To avoid errors

  • Use electrolyte-balanced heparin to avoid bias on electrolytes
  • Use dry heparin to avoid dilution of the blood gas sample and bias on electrolytes and metabolites

Read more

References

Risk of clots

Illustration

Clots in the sample can potentially lead to blocking of the sample pathway on the analyzer and to inaccurate values [1].

Clots can be caused by

  • Too low concentration of heparin in the sample
  • Lack of or insufficient mixing of the sample immediately after it has been collected

Heparin concentration:

The use of heparin as an anticoagulant is needed to reduce clotting of the blood gas sample. However, too much heparin can cause bias on electrolyte values [1]. The use of electrolyte-balanced heparin, instead of traditional heparin, enables the use of a high heparin concentration, reducing the risk of clotting.

Dissolve heparin:

Heparin needs to be dissolved in the blood immediately after the sample is collected. This is obtained by gently mixing the sample right after the sample is collected, and very importantly, after having expelled possible air bubbles.

Clots can lead to

  • Analyzer downtime
  • Potentially inaccurate values – both for the clotted sample, but also for successive samples

To avoid errors

  • Use sufficient concentration of heparin, particularly for samples with a high risk of clotting
  • Use preheparinized syringes containing dry electrolyte-balanced heparin
  • After collecting the sample and expelling possible air bubbles, mix the sample to dissolve the heparin; ensure this is a part of your local procedure

References

Room air contamination

Illustration

Room air contamination of a blood gas sample may alter the values of the sample so that it no longer represents patient status.

The actual bias introduced will have most impact on pO2 and a minor effect on pCO2 and pH [1]. Furthermore the bias on pO2 is highly dependent on volume of room air, initial pO2 value, hemoglobin concentration, mixing of sample and pneumatic tube transport etc [1, 2]. In general, results obtained from capillary samples – particularly pO2 values – should be interpreted with great caution.

Examples

  • Two samples are collected from the same patient and measured after 5 minutes. One sample is mixed and air bubbles expelled, the other is not. This may alter patient results as shown below.
Table
  • 0.2 mL of air is added to a blood gas sample and transported via pneumatic tube. The initial pO2 value is 105 mmHg. After the pneumatic tube transport the pO2 increases to 150 mmHg [2].

To avoid errors

  • Visually inspect the sample for air bubbles
  • Expel any bubbles by gently tapping the sides of the syringe right after sampling and before mixing
  • Use arterial blood gas syringes with tip caps that are vented and will allow you to expel air and seal the syringe without getting in contact with blood

References

  1. Toffaletti J. Effect of small air bubbles on changes in blood pO2 and blood gas parameters: calculated vs. measured effects. www.acutecaretesting.org Jul 2012.
  2. Higgins C. Pneumatic tube transport of samples for blood gas analysis. www.acutecaretesting.org Jan 2005.

Sample mixing

Samples that are thoroughly mixed and rendered homogenous are a prerequisite for reflecting correct patient results [1].

Mixing prior to analysis is performed to achieve a uniform distribution of red blood cells. Insufficient mixing gives erroneous hemoglobin and Hct values and bias on calculated parameters derived from ctHb.

Some studies recommend automatic mixing for consistently achieving homogenous samples [2].

Nonhomogeneous samples can be caused by:

  • Sedimentation of red blood cells
  • No standardized procedure for mixing
  • Sampling devices used are not optimal for mixing e.g. syringes with a narrow diameter may make mixing more difficult

Example

Two samples are stored for 10 minutes before analysis. Red blood cell sedimentation is visible. One sample is mixed thoroughly, the other just long enough to make it appear homogeneous. This may alter patient results as shown below.

Table

To avoid errors

  • Thoroughly mix the sample by inverting the syringe several times and rolling it between the palms of your hands. Red blood cells tend to stack one on top of the other. Stacking is prevented by mixing in two dimensions [3].
  • If the sample is visibly sedimented, it needs mixing for several minutes [2, 3].
  • Ensure a dedicated procedure for sufficient mixing is established and followed in your facility
  • Use blood gas analyzers with effective automatic mixing prior to measurement [2].
  • Use arterial blood gas syringes with an integrated mixing ball when available [1].
Illustration

References

Hemolysis

Hemolysis is the rupture of the red blood cells. The rupture causes the intracellular components of the destroyed red blood cells to be mixed with the plasma. Some of the components, e.g. potassium (K+), are up to 30 times more concentrated in the intracellular compartment than in the plasma phase. Therefore, the potassium measurement will be highly affected by hemolysis.

Hemolysis of as few as 0.5 % of the erythrocytes from a specimen (~0.07 g/dL or 0.05 mmol/L free hemoglobin) can increase the cK+ by 0.5 mmol/L [1].

Illustration

Hemolysis can be caused by

  • Excessive high sample fill rate
  • Vigorous mixing of the sample
  • Accidentally dropping the sample on the floor
  • Cooling the sample on ice

Hemolysis of the sample can lead to

  • Bias on patient results
  • Possible patient misdiagnosis
  • Possible erroneous patient treatment

Example

Two blood gas samples are collected from the same patient. One is analyzed immediately, the other stored for 25 minutes on ice cubes, resulting in 5 % hemolysis and a false increase in cK+ of 3 mmol/L. This may alter patient results as shown below.

Table

To avoid errors

  • Use self-filling blood gas syringes
  • Follow recommended procedures for mixing of samples
  • Use automatic mixing of blood gas samples, if available
  • Store the sample at room temperature (plastic syringes)

Read more

References

Storage temperature

Illustration

Wrong storage temperature of a sample may affect patient results.

The recommended storage temperature of a sample is dependent on the material of the sampling device:

  • plastic sampling devices should be stored at room temperature [1,2]
  • glass sampling devices can be stored in ice slurry water or at room temperature [1,2]

Thus, when storing a sample, please check whether the sampling device is made of plastic or glass and store the sample according to the package insert.

Example

A blood gas sample obtained in a plastic syringe is erroneously stored in ice slurry water which is the recommendation for glass syringes. The initial pO2 is 90 mmHg (12.0 kPa) and when measured after 30 minutes of storage in the ice slurry water the pO2 may have increased to 96 mmHg (12.8 kPa).

To avoid errors

  • Follow specific procedures given by package insert

Read more

References

Storage time

Illustration

After sampling, metabolism continues to take place in the blood gas sample. Delayed analysis increases the risk that test results no longer represent patient status.

Biochemistry predicts the following changes caused by continued metabolism of heparinized arterial blood gas samples obtained anaerobically and stored at room temperature [1]:

Table1

Example

Two samples are collected from the same patient. One is analyzed immediately after collecting the sample, the other after 60 minutes of storage at room temperature. This may alter patient results as shown below.

Table2

To avoid errors

  • Measure the sample immediately [1,2]
  • If storage is unavoidable, measure the sample within 30 minutes [1,2]
  • Measure special samples within 5 minutes: high pO2, high leukocyte count, shunt studies etc; consider using glass sampling devices [1,2]
  • Use a blood gas analyzer that can keep track of sample age

References

Identification of the patient must be done before collecting the sample. How many patient identifiers are recommended to use?

  1. At least one patient identifier

  2. At least two patient identifiers

  3. At least three patient identifiers

Your answer was:
CORRECT!

To avoid patient-sample mix-ups, the use of at least two patient identifiers is recommended, e.g. patient’s name and date of birth or an accession number.

Your answer was:
WRONG!

To avoid patient-sample mix-ups, the use of at least two patient identifiers is recommended, e.g. patient’s name and date of birth or an accession number.

Your answer was:
CORRECT!

Missing or incorrect patient-sample identification can lead to possible misdiagnosis of a patient’s condition.

Your answer was:
WRONG!

Missing or incorrect patient-sample identification can lead to possible misdiagnosis of a patient’s condition.

To avoid the risk of patient-sample mix-ups, make sure a patient ID label is attached to the sample before you leave the patient.

Attach the barcode label:

  1. Either vertically or horizontally

  2. Horizontally on the syringe

  3. Vertically on the syringe

Your answer was:
CORRECT!

Attach the barcode label vertically on the syringe.

Your answer was:
WRONG!

Attach the barcode label vertically on the syringe.

When doing arterial punctures, there is a risk of accidentally puncturing a vein. Even a few drops of venous blood mixed with the arterial sample can lead to:

  1. Bias on O2- and CO2-related parameters

  2. Bias on CO2-related parameters

  3. Bias on O2-related parameters

Your answer was:
CORRECT!

Venous contamination of an arterial blood gas sample can lead to bias on both O2- and CO2-related parameters.

Your answer was:
WRONG!

Venous contamination of an arterial blood gas sample can lead to bias on both O2- and CO2-related parameters.

The use of liquid heparin in blood gas sampling devices can have a bias on:

  1. Electrolytes and metabolites

  2. Electrolytes

  3. Metabolites

Your answer was:
CORRECT!

The use of liquid heparin in blood gas sampling devices can have a bias on electrolytes and metabolites.

Your answer was:
WRONG!

The use of liquid heparin in blood gas sampling devices can have a bias on electrolytes and metabolites.

Your answer was:
CORRECT!

The higher the heparin concentration, the more pronounced the bias on ionized calcium.

Your answer was:
WRONG!

The higher the heparin concentration, the more pronounced the bias on ionized calcium.

Your answer was:
CORRECT!

Use of liquid heparin will inevitably, in contrast to the use of dry heparin, lead to dilution of the blood sample and impact metabolite and electrolyte values.

Your answer was:
WRONG!

Use of liquid heparin will inevitably, in contrast to the use of dry heparin, lead to dilution of the blood sample and impact metabolite and electrolyte values.

Your answer was:
CORRECT!

To avoid heparin-induced bias on test results, use electrolyte-balanced heparin to avoid bias on electrolytes and dry heparin to avoid dilution of the blood sample and bias on electrolytes and metabolites.

Your answer was:
WRONG!

To avoid heparin-induced bias on test results, use electrolyte-balanced heparin to avoid bias on electrolytes and dry heparin to avoid dilution of the blood sample and bias on electrolytes and metabolites.

Your answer was:
CORRECT!

Clots in a blood gas sample can be caused by too low concentration of heparin in the sample as well as lack of or insufficient mixing of the sample after it has been collected.

Your answer was:
WRONG!

Clots in a blood gas sample can be caused by too low concentration of heparin in the sample as well as lack of or insufficient mixing of the sample after it has been collected.

Your answer was:
CORRECT!

Clots in a blood gas sample can lead to analyzer downtime.

Your answer was:
WRONG!

Clots in a blood gas sample can lead to analyzer downtime.

Your answer was:
CORRECT!

To reduce the risk of clots, use a sufficient concentration of heparin, particularly for samples with a high risk of clotting.

Your answer was:
WRONG!

To reduce the risk of clots, use a sufficient concentration of heparin, particularly for samples with a high risk of clotting.

Insufficient mixing can cause coagulation of the sample. Therefore it's recommended to mix the blood sample thoroughly with heparin.

After collecting the sample, what should you do first?

  1. First mix the sample thoroughly and then expel any air bubbles

  2. You can either mix the sample or expel any air bubbles

  3. First expel any air bubbles and then mix the sample thoroughly

Your answer was:
CORRECT!

After collecting a blood gas sample, first expel any air bubbles and then mix it thoroughly.

Your answer was:
WRONG!

After collecting a blood gas sample, first expel any air bubbles and then mix it thoroughly.

The presence of air bubbles in a blood gas sample may alter its values, so that it no longer represents patient status.

The actual bias introduced will have most impact on:

  1. pCO2 and a minor effect on pO2 and pH

  2. pO2 and a minor effect on pCO2 and pH

  3. pH and a minor effect on pCO2 and pO2

Your answer was:
CORRECT!

The presence of air bubbles in a blood gas sample will have most impact on pO2 and a minor effect on pCO2 and pH.

Your answer was:
WRONG!

The presence of air bubbles in a blood gas sample will have most impact on pO2 and a minor effect on pCO2 and pH.

Mixing of a blood gas sample prior to analysis is performed to achieve a uniform distribution of red blood cells.

Insufficient mixing gives erroneous:

  1. Hemoglobin, ctHb and Hct values

  2. Calculated parameters derived from ctHb

  3. Hemoglobin, ctHb, Hct values and bias on calculated parameters derived from ctHb

Your answer was:
CORRECT!

Insufficient mixing of blood gas samples gives erroneous hemoglobin, ctHb, Hct values and bias on calculated parameters derived from ctHb.

Your answer was:
WRONG!

Insufficient mixing of blood gas samples gives erroneous hemoglobin, ctHb, Hct values and bias on calculated parameters derived from ctHb.

Your answer was:
CORRECT!

To ensure correct mixing of a blood gas sample, mix the sample for one minute in two dimensions by rolling the syringe between your hands and by inverting it vertically.

Your answer was:
WRONG!

To ensure correct mixing of a blood gas sample, mix the sample for one minute in two dimensions by rolling the syringe between your hands and by inverting it vertically.

Your answer was:
CORRECT!

Hemolysis can be caused by vigorous mixing of the sample.

Your answer was:
WRONG!

Hemolysis can be caused by vigorous mixing of the sample.

Hemolysis is the rupture of the red blood cells. The rupture causes the intracellular components of the destroyed red blood cells to be mixed with the plasma.

Which parameter is the most affected by this:

  1. cCa2+

  2. cK+

  3. K+

Your answer was:
CORRECT!

Potassium (K+) is up to 30 times more concentrated in the intracellular compartment than it is in the plasma phase. Therefore, the potassium measurement will be highly affected by hemolysis.

Your answer was:
WRONG!

Potassium (K+) is up to 30 times more concentrated in the intracellular compartment than it is in the plasma phase. Therefore, the potassium measurement will be highly affected by hemolysis.

Your answer was:
CORRECT!

To avoid hemolysis in arterial blood gas samples, use self-filling blood gas syringes and store the sample at room temperature.

Your answer was:
WRONG!

To avoid hemolysis in arterial blood gas samples, use self-filling blood gas syringes and store the sample at room temperature.

The recommended storage temperature of a blood gas sample is dependent on the material of the sampling device.

Plastic sampling devices should be stored at:

  1. Slightly warmer than room temperature

  2. On ice

  3. Room temperature

Your answer was:
CORRECT!

Plastic sampling devices containing a blood gas sample should be stored at room temperature.

Your answer was:
WRONG!

Plastic sampling devices containing a blood gas sample should be stored at room temperature.

Storage time can affect patient sample results.

Therefore, it is best to:

  1. Measure the sample within 60 minutes

  2. Measure the sample within 30 minutes

  3. Measure the sample immediately

Your answer was:
CORRECT!

To avoid errors, it is best to measure the sample immediately. If that’s not possible, be sure to analyze the sample within 30 minutes.

Your answer was:
WRONG!

To avoid errors, it is best to measure the sample immediately. If that’s not possible, be sure to analyze the sample within 30 minutes.

Heparin is the only anticoagulant that is recommended for blood gas analysis. This statement is:

  1. True

  2. False

  3. Irrelevant. The use of heparin is not necessary in blood gas testing

Your answer was:
CORRECT!

This statement is true: Heparin is the only anticoagulant that is recommended for blood gas analysis.

Your answer was:
WRONG!

This statement is true: Heparin is the only anticoagulant that is recommended for blood gas analysis.

Troubleshooting

Exceptionally high or low values of a given parameter may be due to one or several types of preanalytical errors. To find out more, select from the menu on the left whether the blood gas sample was collected through an arterial puncture, an arterial line or by capillary sampling.

Then, select a parameter and whether you are experiencing a particularly high (arrow up) or low (arrow down) value.

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Handbook

In the handbook section of this site, you will learn more about proper sampling techniques for arterial puncture, arterial line and capillary sampling and get tips on how to avoid preanalytical errors in blood gas testing.

To begin, select the type of blood gas testing you are interested in learning more about from the menu on the left.

Sampling techniques

Illustration

The purpose of sampling from an arterial line is to obtain an arterial blood gas.

The recommendations shown here are based on best practices and international guidelines. Be sure to follow local procedures.

Preparing for an arterial line sample

Make sure to have all necessary utensils ready before entering the patient room.

Mail me the checklist

Collecting an arterial line sample

Sampling device

Illustration

Selecting the right sampling device for arterial line testing can help reduce the risk of preanalytical errors in blood gas testing.

Therefore, when selecting a device:

  • Use self-filling syringes: they are easier to operate and help ensure sample integrity.
  • Select preheparinized syringes with a sufficiently high concentration of heparin to reduce the risk of clots.
  • Opt for blood gas syringes preheparinized with dry electrolyte-balanced heparin to reduce the risk of electrolyte bias and sample dilution.
  • Select prebarcoded syringes to reduce the risk of patient-sample mix-ups.
  • Choose syringes that come with a tip cap that is vented to ensure the safe removal of air bubbles and to avoid contact with patient blood.
  • Use automatic mixing of samples to ensure sample integrity.

Patient & sample ID

Incorrect or missing patient and sample IDs are some of the most frequent - and critical - preanalytical errors occurring in blood gas testing [1].

Errors can be caused by

  • Lack of patient identification and/or sample labeling
  • Transcription errors due to manual data entry
  • Lack of a dedicated procedure for identifying patient and samples

Errors can lead to

  • Noncompliance with local and national regulatory requirements
  • Misdiagnosis of a patient’s condition
  • Incorrect treatment of a patient
  • Need for resampling, which is both costly and time-consuming
  • Lost billing opportunities from tests that cannot be accounted for

To avoid errors

  • Use at least two patient identifiers when collecting arterial samples [2], e.g. patient’s name and date of birth or an accession number
  • Make sure the arterial syringe has a patient ID label attached to it before you leave the patient
  • Use a prebarcoded arterial syringe, if available
  • Always enter a patient ID into the analyzer before analysis
  • Use barcode readers whenever available – both for bedside identification and at the analyzer – to avoid transcription errors

Attach the barcode label vertically on the syringe as shown below.

Illustration

References

Sample contamination

Illustration

When sampling from an arterial line, there is a risk of diluting the blood gas sample with flush solution. The degree and frequency of this problem is highly dependent on the specific catheter.

If an insufficient amount of flush solution is removed, it will cause increased cNa+ and cCl- values as flush solution contains sodium chloride. The bias affecting pO2 will depend on the actual patient pO2 values. Other parameters will typically be negatively biased.

Example

A sample is collected from an arterial line. One operator removes the flush solution with 1 time the dead space volume of the catheter; the other 6 times. If an insufficient amount of flush solution is removed, the blood gas sample is diluted. See below how this can affect patient results.

Table

To avoid errors

  • Check the specific catheter package for the exact volume of dead space
  • As a rule of thumb, discard at least three times the dead space when you are sampling from catheters
  • Collect the blood gas sample with a dedicated blood gas syringe containing dry electrolyte-balanced heparin
  • If in doubt, consider resampling

Read more

Heparin-induced bias

Illustration

The use of non-compensated heparin in blood gas syringes can cause a bias on electrolytes and metabolites, which ultimately may impact patient treatment [1]. The bias on the electrolytes and metabolites will likely be unidentified and variable; however, it can be avoided.

Heparin is the only anticoagulant that is recommended for blood gas analysis [2]. The use of heparin as an anticoagulant is needed to reduce the clotting of the blood gas sample. Clots in the sample may interfere with the analyzer and produce inaccurate values [3].

Bias on electrolytes may be caused by:

  • Heparin that is not formulated to reduce bias on electrolytes
  • The use of liquid heparin

Formulation of heparin:

Heparin binds to positive ions. This effect has most impact on the concentration of ionized calcium in blood: The higher the heparin concentration, the more pronounced the bias. IFCC states that if heparin concentrations above 15 IU/mL are needed, heparin should be formulated to compensate for the bias on electrolytes [4]. This special heparin formulation, which does not cause bias on electrolytes, is called compensated or electrolyte- balanced. Using electrolyte-balanced heparin allows the usage of a higher concentration of heparin to reduce the likelihood of clotting .

Liquid heparin:

Heparin can be formulated both as a dry heparin and as liquid heparin. Use of liquid heparin will inevitably, in contrast to the use of dry heparin, lead to dilution of the blood gas sample and impact electrolyte and metabolite values.

The dilution effect will vary from sample to sample, depending on the volume of liquid heparin versus the volume of the blood gas sample.

If the volume of liquid heparin is 0.05 mL and 1 mL whole blood is sampled (Hct 45 %) it will dilute the plasma phase by approx. 10 %. Since the electrolytes and metabolites are measured in plasma, the concentrations of these parameters will decrease accordingly.

Examples of heparin-induced bias

Due to the formulation of heparin:

  1. Non-compensated heparin may cause an error on cCa2+ of as much as 6 %. This means that a sample with a true cCa2+ of 1.15 mmol/L (4.6 mg/dL) will report a value that is 0.07 mmol/L (0.28 mg/dL)too low – that corresponds to 50% of the reference range (1.15-1.29 mmol/L (4.6-5.2 mg/dL)) [1].
  2. A non-compensated heparin concentration of 15 IU/mL blood, for example, causes an approximate 0.03 mmol/L (0.12 mg/dL) reduction in ionized calcium. This negative bias rises to 0.15 mmol/L (0.6 mg/dL) with a heparin concentration of 50 IU/mL and to 0.19 mmol/L (0.76 mg/dL) if the heparin concentration is 100 IU/mL [5, 6]. The typical reference range for ionized calcium is 1.15-1.29 mmol/L (4.6-5.2 mg/dL).

Due to liquid heparin:

  1. If the dilution of the sample with liquid heparin is of approximately 10%, true glucose of 5 mmol/L will be measured and yet be reported to be 4.5 mmol/L (81 mg/dL). The same applies to sodium: true sodium of 140 mmol/L will be measured and yet, due to the dilution caused by the use of liquid heparin, be reported to be 126 mmol/L.

To avoid errors

  • Use electrolyte-balanced heparin to avoid bias on electrolytes
  • Use dry heparin to avoid dilution of the blood gas sample and bias on electrolytes and metabolites

Read more

References

Risk of clots

Illustration

Clots in the sample can potentially lead to blocking of the sample pathway on the analyzer and to inaccurate values [1].

Clots can be caused by

  • Too low concentration of heparin in the sample
  • Lack of or insufficient mixing of the sample immediately after it has been collected

Heparin concentration:

The use of heparin as an anticoagulant is needed to reduce clotting of the blood gas sample. However, too much heparin can cause bias on electrolyte values [1]. The use of electrolyte-balanced heparin, instead of traditional heparin, enables the use of a high heparin concentration, reducing the risk of clotting.

Dissolve heparin:

Heparin needs to be dissolved in the blood immediately after the sample is collected. This is obtained by gently mixing the sample right after the sample is collected, and very importantly, after having expelled possible air bubbles.

Clots can lead to

  • Analyzer downtime
  • Potentially inaccurate values – both for the clotted sample, but also for successive samples

To avoid errors

  • Use sufficient concentration of heparin, particularly for samples with a high risk of clotting
  • Use preheparinized syringes containing dry electrolyte-balanced heparin
  • After collecting the sample and expelling possible air bubbles, mix the sample to dissolve the heparin; ensure this is a part of your local procedure

References

Room air contamination

Illustration

Room air contamination of a blood gas sample may alter the values of the sample so that it no longer represents patient status.

The actual bias introduced will have most impact on pO2 and a minor effect on pCO2 and pH [1]. Furthermore the bias on pO2 is highly dependent on volume of room air, initial pO2 value, hemoglobin concentration, mixing of sample and pneumatic tube transport etc [1, 2]. In general, results obtained from capillary samples – particularly pO2 values – should be interpreted with great caution.

Examples

  • Two samples are collected from the same patient and measured after 5 minutes. One sample is mixed and air bubbles expelled, the other is not. This may alter patient results as shown below.
Table
  • 0.2 mL of air is added to a blood gas sample and transported via pneumatic tube. The initial pO2 value is 105 mmHg. After the pneumatic tube transport the pO2 increases to 150 mmHg [2].

To avoid errors

  • Visually inspect the sample for air bubbles
  • Expel any bubbles by gently tapping the sides of the syringe right after sampling and before mixing
  • Use arterial blood gas syringes with tip caps that are vented and will allow you to expel air and seal the syringe without getting in contact with blood

References

  1. Toffaletti J. Effect of small air bubbles on changes in blood pO2 and blood gas parameters: calculated vs. measured effects. www.acutecaretesting.org. July 2012.

Sample mixing

Samples that are thoroughly mixed and rendered homogenous are a prerequisite for reflecting correct patient results [1].

Mixing prior to analysis is performed to achieve a uniform distribution of red blood cells. Insufficient mixing gives erroneous hemoglobin and Hct values and bias on calculated parameters derived from ctHb.

Some studies recommend automatic mixing for consistently achieving homogenous samples [2].

Nonhomogeneous samples can be caused by

  • Sedimentation of red blood cells
  • No standardized procedure for mixing
  • Sampling devices used are not optimal for mixing e.g. syringes with a narrow diameter may make mixing more difficult

Example

Two samples are stored for 10 minutes before analysis. Red blood cell sedimentation is visible. One sample is mixed thoroughly, the other just long enough to make it appear homogeneous. This may alter patient results as shown below.

Table

To avoid errors

  • Thoroughly mix the sample by inverting the syringe several times and rolling it between the palms of your hands. Red blood cells tend to stack one on top of the other. Stacking is prevented by mixing in two dimensions [3].
  • If the sample is visibly sedimented, it needs mixing for several minutes [2, 3].
  • Ensure a dedicated procedure for sufficient mixing is established and followed in your facility
  • Use blood gas analyzers with effective automatic mixing prior to measurement [2].
  • Use arterial blood gas syringes with an integrated mixing ball when available [1].
Illustration

References

Hemolysis

Hemolysis is the rupture of the red blood cells. The rupture causes the intracellular components of the destroyed red blood cells to be mixed with the plasma. Some of the components, e.g. potassium (K+), are up to 30 times more concentrated in the intracellular compartment than in the plasma phase. Therefore, the potassium measurement will be highly affected by hemolysis.

Hemolysis of as few as 0.5 % of the erythrocytes from a specimen (~0.07 g/dL or 0.05 mmol/L free hemoglobin) can increase the cK+ by 0.5 mmol/L [1].

Illustration

Hemolysis can be caused by:

  • Excessive high sample fill rate
  • Vigorous mixing of the sample
  • Accidentally dropping the sample on the floor
  • Cooling the sample on ice

Hemolysis of the sample can lead to:

  • Bias on patient results
  • Possible patient misdiagnosis
  • Possible erroneous patient treatment

Example

Two blood gas samples are collected from the same patient. One is analyzed immediately, the other stored for 25 minutes on ice cubes, resulting in 5 % hemolysis and a false increase in cK+ of 3 mmol/L. This may alter patient results as shown below.

Table

To avoid errors

  • Use self-filling blood gas syringes
  • Follow recommended procedures for mixing of samples
  • Use automatic mixing of blood gas samples, if available
  • Store the sample at room temperature (plastic syringes)

Read more

References

Storage temperature

Illustration

Wrong storage temperature of a sample may affect patient results.

The recommended storage temperature of a sample is dependent on the material of the sampling device:

  • plastic sampling devices should be stored at room temperature [1,2]
  • glass sampling devices can be stored in ice slurry water or at room temperature [1,2]

Thus, when storing a sample, please check whether the sampling device is made of plastic or glass and store the sample according to the package insert.

Example

A blood gas sample obtained in a plastic syringe is erroneously stored in ice slurry water which is the recommendation for glass syringes. The initial pO2 is 90 mmHg (12.0 kPa) and when measured after 30 minutes of storage in the ice slurry water the pO2 may have increased to 96 mmHg (12.8 kPa).

To avoid errors

  • Follow specific procedures given by package insert

Read more

References

Storage time

Illustration

After sampling, metabolism continues to take place in the blood gas sample. Delayed analysis increases the risk that test results no longer represent patient status.

Biochemistry predicts the following changes caused by continued metabolism of heparinized arterial blood gas samples obtained anaerobically and stored at room temperature [1]:

Table 1

Example

Two samples are collected from the same patient. One is analyzed immediately after collecting the sample, the other after 60 minutes of storage at room temperature. This may alter patient results as shown below.

Table 2

To avoid errors

  • Measure the sample immediately [1,2]
  • If storage is unavoidable, measure the sample within 30 minutes [1,2]
  • Measure special samples within 5 minutes: high pO2, high leukocyte count, shunt studies etc; consider using glass sampling devices [1,2]
  • Use a blood gas analyzer that can keep track of sample age

References

Identification of the patient must be done before collecting the sample. How many patient identifiers are recommended to use?

  1. At least two patient identifiers

  2. At least three patient identifiers

  3. At least one patient identifier

Your answer was:
CORRECT!

To avoid patient-sample mix-ups, the use of at least two patient identifiers is recommended, e.g. patient’s name and date of birth or an accession number.

Your answer was:
WRONG!

To avoid patient-sample mix-ups, the use of at least two patient identifiers is recommended, e.g. patient’s name and date of birth or an accession number.

Your answer was:
CORRECT!

Missing or incorrect patient-sample identification can lead to possible misdiagnosis of a patient’s condition.

Your answer was:
WRONG!

Missing or incorrect patient-sample identification can lead to possible misdiagnosis of a patient’s condition.

To avoid the risk of patient-sample mix-ups, make sure a patient ID label is attached to the sample before you leave the patient.

Attach the barcode label:

  1. Horizontally on the syringe

  2. Vertically on the syringe

  3. Either vertically or horizontally

Your answer was:
CORRECT!

Attach the barcode label vertically on the syringe.

Your answer was:
WRONG!

Attach the barcode label vertically on the syringe.

Your answer was:
CORRECT!

If insufficient flush solution is removed, this will cause a positive bias on cNa+ and cCl- as flush solution contains sodium chloride. The bias affecting pO2 will depend on the actual patient pO2 values.

Your answer was:
WRONG!

If insufficient flush solution is removed, this will cause a positive bias on cNa+ and cCl- as flush solution contains sodium chloride. The bias affecting pO2 will depend on the actual patient pO2 values.

The use of liquid heparin in blood gas sampling devices can have a bias on:

  1. Metabolites

  2. Electrolytes and metabolites

  3. Electrolytes

Your answer was:
CORRECT!

The use of liquid heparin in blood gas sampling devices can have a bias on electrolytes and metabolites.

Your answer was:
WRONG!

The use of liquid heparin in blood gas sampling devices can have a bias on electrolytes and metabolites.

Your answer was:
CORRECT!

The higher the heparin concentration, the more pronounced the bias on ionized calcium.

Your answer was:
WRONG!

The higher the heparin concentration, the more pronounced the bias on ionized calcium.

Your answer was:
CORRECT!

Use of liquid heparin will inevitably, in contrast to the use of dry heparin, lead to dilution of the blood sample and impact metabolite and electrolyte values.

Your answer was:
WRONG!

Use of liquid heparin will inevitably, in contrast to the use of dry heparin, lead to dilution of the blood sample and impact metabolite and electrolyte values.

Your answer was:
CORRECT!

To avoid heparin-induced bias on test results, use electrolyte-balanced heparin to avoid bias on electrolytes and dry heparin to avoid dilution of the blood sample and bias on electrolytes and metabolites.

Your answer was:
WRONG!

To avoid heparin-induced bias on test results, use electrolyte-balanced heparin to avoid bias on electrolytes and dry heparin to avoid dilution of the blood sample and bias on electrolytes and metabolites.

Your answer was:
CORRECT!

Clots in a blood gas sample can be caused by too low concentration of heparin in the sample as well as lack of or insufficient mixing of the sample after it has been collected.

Your answer was:
WRONG!

Clots in a blood gas sample can be caused by too low concentration of heparin in the sample as well as lack of or insufficient mixing of the sample after it has been collected.

Your answer was:
CORRECT!

Clots in a blood gas sample can lead to analyzer downtime.

Your answer was:
WRONG!

Clots in a blood gas sample can lead to analyzer downtime.

Your answer was:
CORRECT!

To reduce the risk of clots, use a sufficient concentration of heparin, particularly for samples with a high risk of clotting.

Your answer was:
WRONG!

To reduce the risk of clots, use a sufficient concentration of heparin, particularly for samples with a high risk of clotting.

Insufficient mixing can cause coagulation of the sample. Therefore it's recommended to mix the blood sample thoroughly with heparin.

After collecting the sample, what should you do first?

  1. First expel any air bubbles and then mix the sample thoroughly

  2. First mix the sample thoroughly and then expel any air bubbles

  3. You can either mix the sample or expel any air bubbles

Your answer was:
CORRECT!

After collecting a blood gas sample, first expel any air bubbles and then mix it thoroughly.

Your answer was:
WRONG!

After collecting a blood gas sample, first expel any air bubbles and then mix it thoroughly.

The presence of air bubbles in a blood gas sample may alter its values, so that it no longer represents patient status.

The actual bias introduced will have most impact on:

  1. pO2 and a minor effect on pCO2 and pH

  2. pH and a minor effect on pCO2 and pO2

  3. pCO2 and a minor effect on pO2 and pH

Your answer was:
CORRECT!

The presence of air bubbles in a blood gas sample will have most impact on pO2 and a minor effect on pCO2 and pH.

Your answer was:
WRONG!

The presence of air bubbles in a blood gas sample will have most impact on pO2 and a minor effect on pCO2 and pH.

Mixing of a blood gas sample prior to analysis is performed to achieve a uniform distribution of red blood cells.

Insufficient mixing gives erroneous:

  1. Hemoglobin, ctHb and Hct values

  2. Calculated parameters derived from ctHb

  3. Hemoglobin, ctHb, Hct values and bias on calculated parameters derived from ctHb

Your answer was:
CORRECT!

Insufficient mixing of blood gas samples gives erroneous hemoglobin, ctHb, Hct values and bias on calculated parameters derived from ctHb.

Your answer was:
WRONG!

Insufficient mixing of blood gas samples gives erroneous hemoglobin, ctHb, Hct values and bias on calculated parameters derived from ctHb.

Your answer was:
CORRECT!

To ensure correct mixing of a blood gas sample, mix the sample for one minute in two dimensions by rolling the syringe between your hands and by inverting it vertically.

Your answer was:
WRONG!

To ensure correct mixing of a blood gas sample, mix the sample for one minute in two dimensions by rolling the syringe between your hands and by inverting it vertically.

Your answer was:
CORRECT!

Hemolysis can be caused by vigorous mixing of the sample.

Your answer was:
WRONG!

Hemolysis can be caused by vigorous mixing of the sample.

Hemolysis is the rupture of the red blood cells. The rupture causes the intracellular components of the destroyed red blood cells to be mixed with the plasma.

Which parameter is the most affected by this:

  1. cK+

  2. cCa2+

  3. K+

Your answer was:
CORRECT!

Potassium (K+) is up to 30 times more concentrated in the intracellular compartment than it is in the plasma phase. Therefore, the potassium measurement will be highly affected by hemolysis.

Your answer was:
WRONG!

Potassium (K+) is up to 30 times more concentrated in the intracellular compartment than it is in the plasma phase. Therefore, the potassium measurement will be highly affected by hemolysis.

Your answer was:
CORRECT!

To avoid hemolysis in arterial blood gas samples, use self-filling blood gas syringes and store the sample at room temperature.

Your answer was:
WRONG!

To avoid hemolysis in arterial blood gas samples, use self-filling blood gas syringes and store the sample at room temperature.

The recommended storage temperature of a blood gas sample is dependent on the material of the sampling device.

Plastic sampling devices should be stored at:

  1. Room temperature

  2. On ice

  3. Slightly warmer than room temperature

Your answer was:
CORRECT!

Plastic sampling devices containing a blood gas sample should be stored at room temperature.

Your answer was:
WRONG!

Plastic sampling devices containing a blood gas sample should be stored at room temperature.

Storage time can affect patient sample results.

Therefore, it is best to:

  1. Measure the sample within 30 minutes

  2. Measure the sample within 60 minutes

  3. Measure the sample immediately

Your answer was:
CORRECT!

To avoid errors, it is best to measure the sample immediately. If that’s not possible, be sure to analyze the sample within 30 minutes.

Your answer was:
WRONG!

To avoid errors, it is best to measure the sample immediately. If that’s not possible, be sure to analyze the sample within 30 minutes.

Heparin is the only anticoagulant that is recommended for blood gas analysis. This statement is:

  1. Irrelevant. The use of heparin is not necessary in blood gas testing

  2. True

  3. False

Your answer was:
CORRECT!

This statement is true: Heparin is the only anticoagulant that is recommended for blood gas analysis.

Your answer was:
WRONG!

This statement is true: Heparin is the only anticoagulant that is recommended for blood gas analysis.

Troubleshooting

Exceptionally high or low values of a given parameter may be due to one or several types of preanalytical errors. To find out more, select from the menu on the left whether the blood gas sample was collected through an arterial puncture, an arterial line or by capillary sampling.

Then, select a parameter and whether you are experiencing a particularly high (arrow up) or low (arrow down) value.

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Handbook

In the handbook section of this site, you will learn more about proper sampling techniques for arterial puncture, arterial line and capillary sampling and get tips on how to avoid preanalytical errors in blood gas testing.

To begin, select the type of blood gas testing you are interested in learning more about from the menu on the left.

Sampling techniques

Illustration

One of the purposes of capillary sampling is to obtain a sample for blood gas analysis.

The recommendations shown here are based on best practices and international guidelines. Be sure to follow local procedures.

A puncture or small incision is made with a lancet or similar device into the cutaneous layer of the skin at a highly vascularized area (e.g. heel, earlobe, finger or toe). An automatically retractable device that limits incision depth can be used to achieve an accurate incision depth.

A common procedure, although not universally recommended in the literature, is to warm the sampling site to accelerate blood flow. As the blood flows freely from the incision site, the sample is collected in a heparinized capillary tube.

On neonates, capillary sampling is usually done through an incision on the heel. For children up to 12 months of age, heel incisions can be used, unless the child has begun to walk and develop callus [1].

In general, results obtained from capillary samples – particularly pO2 values – should be interpreted with great caution.

Preparing for a capillary sample

Make sure to have all necessary utensils ready before entering the patient room.

Mail me the checklist

Collecting a capillary sample from a neonate or a child under three months of age

Mail me more information

Collecting a capillary sample from an adult or a child three months of age or older

Mail me more information

References

Sampling device

Illustration

Selecting the right capillary sampling device can help reduce the risk of preanalytical errors in blood gas testing.

Therefore, when selecting a device:

  • Match the capillary tube size with the specific measuring mode chosen on the analyzer.
  • Only preheparinized capillary tubes are recommended for blood gas testing. Heparin in a sufficiently high concentration is vital to ensure that the capillary sample does not coagulate.
  • Use capillary tubes preheparinized with electrolyte-balanced heparin to reduce the risk of electrolyte bias and sample dilution.
  • Use capillary tubes coated with high-concentration sodium heparin for samples with a higher risk of in-vitro clotting, e.g. umbilical cord and fetal scalp samples. Because of the high concentration of heparin, do not report electrolyte values.
  • When breakage of glass is a concern, use plastic capillary tubes instead.
  • Use a mixing wire to help ensure sufficient mixing of the sample.
  • Use capillary tubes with end caps to prevent spillage.

Patient & sample ID

Incorrect or missing patient and sample IDs are some of the most frequent – and critical – preanalytical errors occurring in blood gas testing [1].

Errors can be caused by

  • Lack of patient identification and/or sample labeling
  • Transcription errors due to manual data entry
  • Lack of a dedicated procedure for identifying patient and samples

Errors can lead to

  • Noncompliance with local and national regulatory requirements
  • Misdiagnosis of a patient’s condition
  • Incorrect treatment of a patient
  • Need for resampling, which is both costly and time-consuming
  • Lost billing opportunities from tests that cannot be accounted for

To avoid errors

  • Use at least two patient identifiers when collecting capillary samples [2], e.g. patient’s name and date of birth or an accession number
  • Make sure the capillary tube has an ID label attached to it before you leave the patient
  • Always enter a patient ID into the blood gas analyzer before analysis
  • Use barcode readers whenever available – both for bedside identification and at the analyzer – to avoid transcription errors

Attach the barcode label as shown below.

Illustration

References

Sample contamination

Illustration

During capillary sampling, there is a risk of contamination of the blood gas sample with tissue fluid due to milking or massaging the puncture area to increase the blood flow.

In general, results obtained from capillary samples – particularly pO2 values – should be interpreted with great caution.

Contamination with tissue fluid can lead to

  • Risk that the values no longer represent patient status

A common procedure to avoid this is to warm the sampling site, e.g. the heel. However, this is not universally recommended in the literature. According to the CLSI guidelines [1]: "Although studies show that prewarming may not be necessary when using a skin incision device, increasing blood flow may be necessary to prevent hemolysis and/or contamination with tissue fluids when using other devices or as a general practice."

To avoid errors

  • Carefully evaluate if warming of tissue is relevant or not
  • Avoid milking of tissue during sampling

Read more

References

Heparin-induced bias

Illustration

The use of non-compensated heparin in blood gas syringes can cause a bias on electrolytes and metabolites, which ultimately may impact patient treatment [1]. The bias on the electrolytes and metabolites will likely be unidentified and variable; however, it can be avoided.

Heparin is the only anticoagulant that is recommended for blood gas analysis [2]. The use of heparin as an anticoagulant is needed to reduce the clotting of the blood gas sample. Clots in the sample may interfere with the analyzer and produce inaccurate values [3] (see “reduce the risk of clots”).

Bias on electrolytes may be caused by

  • Heparin that is not formulated to reduce bias on electrolytes
  • The use of liquid heparin

Formulation of heparin:

Heparin binds to positive ions. This effect has most impact on the concentration of ionized calcium in blood: The higher the heparin concentration, the more pronounced the bias. IFCC states that if heparin concentrations above 15 IU/mL are needed, heparin should be formulated to compensate for the bias on electrolytes [4]. This special heparin formulation, which does not cause bias on electrolytes, is called compensated or electrolyte- balanced. Using electrolyte-balanced heparin allows the usage of a higher concentration of heparin to reduce the likelihood of clotting .

Liquid heparin:

Heparin can be formulated both as a dry heparin and as liquid heparin. Use of liquid heparin will inevitably, in contrast to the use of dry heparin, lead to dilution of the blood gas sample and impact electrolyte and metabolite values.

The dilution effect will vary from sample to sample, depending on the volume of liquid heparin versus the volume of the blood gas sample.

If the volume of liquid heparin is 0.05 mL and 1 mL whole blood is sampled (Hct 45 %) it will dilute the plasma phase by approx. 10 %. Since the electrolytes and metabolites are measured in plasma, the concentrations of these parameters will decrease accordingly.

Examples of heparin-induced bias

Due to the formulation of heparin:

  1. Non-compensated heparin may cause an error on cCa2+ of as much as 6 %. This means that a sample with a true cCa2+ of 1.15 mmol/L (4.6 mg/dL) will report a value that is 0.07 mmol/L (0.28 mg/dL)too low – that corresponds to 50% of the reference range (1.15-1.29 mmol/L (4.6-5.2 mg/dL)) [1].
  2. A non-compensated heparin concentration of 15 IU/mL blood, for example, causes an approximate 0.03 mmol/L (0.12 mg/dL) reduction in ionized calcium. This negative bias rises to 0.15 mmol/L (0.6 mg/dL) with a heparin concentration of 50 IU/mL and to 0.19 mmol/L (0.76 mg/dL) if the heparin concentration is 100 IU/mL [5, 6]. The typical reference range for ionized calcium is 1.15-1.29 mmol/L (4.6-5.2 mg/dL).

Due to liquid heparin:

  1. If the dilution of the sample with liquid heparin is of approximately 10%, true glucose of 5 mmol/L will be measured and yet be reported to be 4.5 mmol/L (81 mg/dL). The same applies to sodium: true sodium of 140 mmol/L will be measured and yet, due to the dilution caused by the use of liquid heparin, be reported to be 126 mmol/L.

To avoid errors

  • Use electrolyte-balanced heparin to avoid bias on electrolytes
  • Use dry heparin to avoid dilution of the blood gas sample and bias on electrolytes and metabolites

Read more

References

Risk of clots

Illustration

Clots in the sample can potentially lead to blocking of the sample pathway on the analyzer as well as inaccurate values [1].

Clots can be caused by

  • Too low concentration of heparin in the sample
  • Lack of or insufficient mixing of the sample immediately after it has been collected

Heparin concentration:

The use of heparin as an anticoagulant is needed to reduce clotting of the blood gas sample. However, too much heparin can cause bias on electrolyte values [1]. The use of electrolyte-balanced heparin, instead of traditional heparin, enables the use of a high heparin concentration, reducing the risk of clotting.

Dissolve heparin:

Heparin needs to be dissolved in the blood immediately after the sample is collected. This is obtained by gently mixing the sample right after the sample is collected, and very importantly, after having expelled possible air bubbles.

Clots can lead to

  • Analyzer downtime
  • Potentially inaccurate values – both for the clotted sample, but also for successive samples

To avoid errors

  • Use sufficient concentration of heparin, particularly for samples with a high risk of clotting
  • Use preheparinized capillary tubes containing dry electrolyte-balanced heparin
  • After collecting the sample and expelling possible air bubbles, mix the sample to dissolve the heparin; ensure this is a part of your local procedure

References

Sample mixing

Samples that are thoroughly mixed and rendered homogenous are a prerequisite for reflecting correct patient results [1].

Mixing prior to analysis is performed to achieve a uniform distribution of red blood cells and plasma prior to inserting the sample into the analyzer. Insufficient mixing gives erroneous hemoglobin and Hct and biased calculated parameters derived from ctHb.

Mixing of capillary samples should be done carefully due to the risk of hemolysis (see section on hemolysis). That is particularly true for fragile samples, e.g. from neonates. Too vigorous mixing can result in falsely increased cK+ and decreased cNa+ values [2].

Nonhomogeneous samples can be caused by

  • Sedimentation of red blood cells
  • No standardized procedure for mixing
  • Lack of dedicated mixing device e.g. mixing wire

To avoid errors

  • If the sample is visibly sedimented, it needs mixing for several minutes [2, 3]
  • Use proper devices to ensure sufficient mixing of capillary samples, e.g. mixing wire
  • Ensure a dedicated procedure for sufficient mixing is established and followed in your facility
Illustration

References

Hemolysis

Hemolysis is the rupture of the red blood cells. The rupture causes the intracellular components of the destroyed red blood cells to be mixed with the plasma. Some of the components, e.g. potassium (K+), are up to 30 times more concentrated in the intracellular compartment than in the plasma phase. Therefore, the potassium measurement will be highly affected by hemolysis.

Hemolysis of as few as 0.5 % of the erythrocytes from a specimen (~0.07 g/dL or 0.05 mmol/L free hemoglobin) can increase the cK+ by 0.5 mmol/L [1].

Illustration

Hemolysis can be caused by

  • Squeezing of tissue during capillary sampling
  • Vigorous mixing of the sample
  • Accidentally dropping the sample on the floor
  • Cooling the sample on ice

Hemolysis of the sample can lead to

  • Bias on patient results
  • Possible patient misdiagnosis
  • Possible erroneous patient treatment

Example

Two blood gas samples are collected from the same patient. One is analyzed immediately, the other stored for 25 minutes on ice cubes, resulting in 5 % hemolysis and a false increase in cK+ of 3 mmol/L. This may alter patient results as shown below.

Table

To avoid errors

  • Do not milk or massage the tissue during sampling; increasing the blood flow to the puncture site by warming the tissue may be relevant – see section on Correct sample type
  • Use adequate puncture depth – a maximum of 2 mm is recommended; use caution with neonates [1]
  • Follow recommended procedures for mixing of samples
  • Store the sample at proper temperature – see section on Control storage temperature

Read more

References

Storage temperature

Illustration

Wrong storage temperature of a sample may affect patient results.

The recommended storage temperature of a sample is dependent on the material of the sampling device:

  • plastic sampling devices should be stored at room temperature [1,2]
  • glass sampling devices can be stored in ice slurry water or at room temperature [1,2]

Thus, when storing a sample, please check whether the sampling device is made of plastic or glass and store the sample according to the package insert.

Example

A blood gas sample obtained in a plastic syringe is erroneously stored in ice slurry water which is the recommendation for glass syringes. The initial pO2 is 90 mmHg (12.0 kPa) and when measured after 30 minutes of storage in the ice slurry water the pO2 may have increased to 96 mmHg (12.8 kPa).

To avoid errors

  • Follow specific procedures given by package insert

Read more

References

Storage time

Illustration

After sampling, metabolism continues to take place in the blood gas sample. Delayed analysis increases the risk that test results no longer represent patient status.

Biochemistry predicts the following changes caused by continued metabolism of heparinized arterial blood gas samples obtained anaerobically and stored at room temperature [1]:

Table

Example

Two samples are collected from the same patient. One is analyzed immediately after collecting the sample, the other after 60 minutes of storage at room temperature. This may alter patient results as shown below.

Table

To avoid errors

  • Measure the sample immediately [1,2]
  • If storage is unavoidable, measure the sample within 30 minutes [1,2]
  • Measure special samples within 5 minutes: high pO2, high leukocyte count, shunt studies etc; consider using glass sampling devices [1,2]
  • Use a blood gas analyzer that can keep track of sample age

References

Identification of the patient must be done before collecting the sample. How many patient identifiers are recommended to use?

  1. At least two patient identifiers

  2. At least three patient identifiers

  3. At least one patient identifier

Your answer was:
CORRECT!

To avoid patient-sample mix-ups, the use of at least two patient identifiers is recommended, e.g. patient’s name and date of birth or an accession number.

Your answer was:
WRONG!

To avoid patient-sample mix-ups, the use of at least two patient identifiers is recommended, e.g. patient’s name and date of birth or an accession number.

Your answer was:
CORRECT!

Missing or incorrect patient-sample identification can lead to possible misdiagnosis of a patient’s condition.

Your answer was:
WRONG!

Missing or incorrect patient-sample identification can lead to possible misdiagnosis of a patient’s condition.

To avoid the risk of patient-sample mix-ups, make sure a patient ID label is attached to the sample before you leave the patient.

Attach the barcode label:

  1. Horizontally around the capillary tube

  2. Vertically around the capillary tube

  3. Either vertically or horizontally around the capillary tube

Your answer was:
CORRECT!

Attach the barcode label horizontally around the capillary tube.

Your answer was:
WRONG!

Attach the barcode label horizontally around the capillary tube.

Your answer was:
CORRECT!

To avoid contamination of the capillary blood sample with tissue fluid, avoid milking of the tissue during sampling.

Your answer was:
WRONG!

To avoid contamination of the capillary blood sample with tissue fluid, avoid milking of the tissue during sampling.

Your answer was:
CORRECT!

The higher the heparin concentration, the more pronounced the bias on ionized calcium.

Your answer was:
WRONG!

The higher the heparin concentration, the more pronounced the bias on ionized calcium.

Your answer was:
CORRECT!

To avoid heparin-induced bias on test results, use electrolyte-balanced heparin to avoid bias on electrolytes and dry heparin to avoid dilution of the blood sample and bias on electrolytes and metabolites.

Your answer was:
WRONG!

To avoid heparin-induced bias on test results, use electrolyte-balanced heparin to avoid bias on electrolytes and dry heparin to avoid dilution of the blood sample and bias on electrolytes and metabolites.

Your answer was:
CORRECT!

Clots in a blood gas sample can lead to analyzer downtime.

Your answer was:
WRONG!

Clots in a blood gas sample can lead to analyzer downtime.

Your answer was:
CORRECT!

To reduce the risk of clots, use a sufficient concentration of heparin, particularly for samples with a high risk of clotting.

Your answer was:
WRONG!

To reduce the risk of clots, use a sufficient concentration of heparin, particularly for samples with a high risk of clotting.

To ensure correct mixing of a capillary blood gas sample:

  1. Heat the sample

  2. Use a mixing wire

  3. Roll the capillary tube between your hands

Your answer was:
CORRECT!

Use proper devices to ensure sufficient mixing of capillary samples, e.g. a mixing wire.

Your answer was:
WRONG!

Use proper devices to ensure sufficient mixing of capillary samples, e.g. a mixing wire.

Your answer was:
CORRECT!

Hemolysis in capillary blood gas samples can be caused by cooling the sample on ice.

Your answer was:
WRONG!

Hemolysis in capillary blood gas samples can be caused by cooling the sample on ice.

Hemolysis in capillary blood gas samples can also be caused by:

  1. Insufficient mixing

  2. Accidentally dropping the sample on the floor

  3. Using too much heparin

Your answer was:
CORRECT!

Hemolysis in capillary blood gas samples can also be caused by accidentally dropping the sample on the floor.

Your answer was:
WRONG!

Hemolysis in capillary blood gas samples can also be caused by accidentally dropping the sample on the floor.

The recommended storage temperature of a blood gas sample is dependent on the material of the sampling device.

Plastic sampling devices should be stored at:

  1. Slightly warmer than room temperature

  2. On ice

  3. Room temperature

Your answer was:
CORRECT!

Plastic sampling devices containing a blood gas sample should be stored at room temperature.

Your answer was:
WRONG!

Plastic sampling devices containing a blood gas sample should be stored at room temperature.

Wrong storage temperature of a sample may affect patient results.

The best way to store a blood gas sample in a capillary glass tube is:

  1. In iced water or room temperature

  2. In iced water

  3. At room temperature

Your answer was:
CORRECT!

Samples in capillary glass tubes can be stored either in either iced water or at room temperature.

Your answer was:
WRONG!

Samples in capillary glass tubes can be stored either in either iced water or at room temperature.

Storage time can affect patient sample results.

Therefore, it is best to:

  1. Measure the sample within 60 minutes

  2. Measure the sample immediately

  3. Measure the sample within 30 minutes

Your answer was:
CORRECT!

To avoid errors, it is best to measure the sample immediately. If that’s not possible, be sure to analyze the sample within 30 minutes.

Your answer was:
WRONG!

To avoid errors, it is best to measure the sample immediately. If that’s not possible, be sure to analyze the sample within 30 minutes.

Heparin is the only anticoagulant that is recommended for blood gas analysis. This statement is:

  1. True

  2. Irrelevant. The use of heparin is not necessary in blood gas testing

  3. False

Your answer was:
CORRECT!

This statement is true: Heparin is the only anticoagulant that is recommended for blood gas analysis.

Your answer was:
WRONG!

This statement is true: Heparin is the only anticoagulant that is recommended for blood gas analysis.

Wrong storage temperature of a sample may affect patient results.

The best way to store a blood gas sample in a capillary plastic tube is:

  1. In iced water

  2. In iced water or room temperature

  3. At room temperature

Your answer was:
CORRECT!

Samples in capillary plastic tubes can only be stored at room temperature.

Your answer was:
WRONG!

Samples in capillary plastic tubes can only be stored at room temperature.

When performing a heel incision on a neonate, what is the recommended maximum depth of the incision?

  1. 3 mm

  2. 2 mm

  3. 1 mm

Your answer was:
CORRECT!

When performing a heel incision on a neonate, the recommended maximum depth of the incision is 2 mm.

Your answer was:
WRONG!

When performing a heel incision on a neonate, the recommended maximum depth of the incision is 2 mm.

When performing capillary testing on an adult, what is the recommended minimum-maximum depth of the incision?

  1. 3 - 5 mm

  2. 2 - 4 mm

  3. 1 - 2mm

Your answer was:
CORRECT!

When performing capillary testing on an adult, the recommended minimum-maximum depth of the incision is 2- 4 mm.

Your answer was:
WRONG!

When performing capillary testing on an adult, the recommended minimum-maximum depth of the incision is 2- 4 mm.

Troubleshooting

Exceptionally high or low values of a given parameter may be due to one or several types of preanalytical errors. To find out more, select from the menu on the left whether the blood gas sample was collected through an arterial puncture, an arterial line or by capillary sampling.

Then, select a parameter and whether you are experiencing a particularly high (arrow up) or low (arrow down) value.

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors:

Possible errors: