Objective: The purpose of this study was to determine the effect of timing of analysis, collection tube type and repeated opening of sample tubes on venous PCO2, pH, HCO3, and base excess (BE) results.
Design: Prospective experimental study, paired sample analysis.
Setting: Veterinary Medical Teaching Hospital.
Animals: Twenty dogs.
Interventions: Jugular venous blood samples.
Measurements and main results: PCO2, pH, HCO3, and BE were determined immediately following collection (control) and at selected times up to 30 minutes after placement in either screw top or vacuum heparin collection tubes. A different set of screw top and vacuum heparin collection tubes were sampled repeatedly over time for up to 15 minutes.
In the screw top delayed analysis group, only pH changed significantly at one time point. PCO2 decreased significantly in all other groups and resulted in a significant reciprocal pH change in the vacuum tubes with either delayed single analysis or repeated sampling. HCO3 and BE declined significantly in multi-sampled vacuum tubes and HCO3 also decreased significantly in multi-sampled screw top tubes.
Conclusions: Analysis of acid–base status is optimally performed on freshly drawn blood. However, when it is anticipated there will be a delay in analysis of samples kept at room temperature, the use of 2.0 mL plastic screw top heparin anticoagulant tubes may result in fewer pre-analytical errors than 3.5 mL glass vacuum tubes.