Impact of blood volume, air exposure duration, transport duration, and testing delay on plasma total carbon dioxide in simulated open collections using microtainers

Background

Exposing blood specimens to air reduces plasma total carbon dioxide (TCO₂). We evaluated the degree of TCO₂ reduction attributed to open collection of neonatal blood in BD microtainers® (microtainers), microtainer transport duration and delayed testing of open plasma aliquots.

Methods

Venous blood was aliquoted into open microtainers in a 3x4 factorial design to simulate combined effects of blood volume (0.2–0.6 mL) and air exposure duration (0–5 min), with blood drawn in vacutainers as a control. Separate effects of in-hospital transport duration (0–120 min; whole blood), off-site transport duration (0–24 h; centrifuged whole blood), and the duration plasma aliquots remained open (0–120 min) were evaluated by repeated testing. Findings were analyzed using repeated-measures ANOVA and Student’s T-tests.

Results

In the factorial experiment, mean plasma TCO₂ in microtainers was on average 3.5 mmol/L lower than in vacutainers. Smaller blood volume but not greater air exposure duration significantly (p < 0.05) reduced TCO₂. Mean TCO₂ in filled (0.6 mL; 1–5 min air exposure) microtainers was on average 2.9 mmol/L lower than in vacutainers. Simulated off-site transport of microtainers containing centrifuged whole blood significantly reduced TCO₂ (4 h; mean change = -1.5 mmol/L), as did delayed testing of aliquoted plasma (15 min; mean change = -1.3 mmol/L).

Conclusions

Plasma TCO₂ decreased with reduced microtainer blood volume, extended off-site transport duration of centrifuged whole blood and testing delay of aliquoted plasma. To minimize TCO₂ reduction, microtainers should be fully filled and tested rapidly. Laboratories should also consider whether an interpretive comment, correction factor or separate reference intervals are appropriate for these tests.