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Artefactual reduction in plasma total carbon dioxide concentration in children
Andrew J Williams1, Lisa Norris, John C Coakley
1Department of Clinical Immunology, Royal Prince Alfred Hospital, Camperdown, Australia. awilliams@immu.rpa.cs.nsw.gov.au
Insights
Collecting small blood volumes in large tubes significantly decreases plasma total carbon dioxide (ctCO2). Use smaller tubes with minimal air space for accurate ctCO2 measurements, especially with limited sample volumes.
Area of Science:
- Clinical Chemistry
- Laboratory Medicine
- Pediatric Diagnostics
Background:
- Accurate measurement of plasma total carbon dioxide (ctCO2) is crucial for diagnosing acid-base imbalances.
- Sample collection methods can influence laboratory test results.
- Previous observations suggested potential issues with small blood volumes in large collection tubes.
Purpose of the Study:
- To investigate the impact of collecting small blood volumes into large tubes on plasma ctCO2 levels.
- To determine the extent of ctCO2 alteration based on sample volume and air space.
- To provide recommendations for optimal blood sample collection for ctCO2 analysis.
Main Methods:
- Blood samples were collected from three volunteers on five separate occasions.
- Various volumes of blood were placed into 4-mL tubes.
- Samples were analyzed after different time intervals to assess ctCO2 stability.
Main Results:
- A significant decrease in plasma ctCO2 was observed when the collected blood volume was less than 2 mL.
- A 42% reduction in ctCO2 was recorded in a 0.3 mL sample within a 4-mL tube after 4 hours.
- The volume of air space in the collection tube correlated with the observed decrease in ctCO2.
Conclusions:
- Collecting small blood volumes in large tubes leads to a significant decrease in plasma ctCO2.
- Recommendations include using smaller collection tubes with minimal air space when only a small blood sample is available.
- Adhering to these collection guidelines ensures the accuracy of ctCO2 measurements in clinical practice.
Methods:
The effect on plasma total carbon dioxide (ctCO2) of collecting a small volume of blood into a large tube was investigated. In a 7-month-old infant presenting with diarrhoea the initial ctCO2 was low when 0.3 mL of sample was received in a 4-mL tube. To investigate this further blood samples were obtained from three volunteers on five occasions and various volumes were placed in a 4 mL container and analysed after varying intervals.
Results:
When the sample volume was less than 2 mL there was a significant decrease in ctCO2. A 42% decrease was seen in the tube containing 0.3 mL after 4 h.
Conclusions:
We recommend that when a small volume of sample is collected it should be placed in a smaller tube with minimal air space.