Abstract
Objective—To determine whether plasma total CO2 concentrations would vary with the size of the evacuated tube used to collect blood samples.
Design—Randomized crossover study.
Animals—Convenience sample of 20 healthy adult horses.
Procedures—Jugular venous blood was collected from horses in random order into 8 types of evacuated tubes: 2-mL glass, 2- or 3-mL plastic or plastic plasma separator, 4- or 6-mL plastic, and 10-mL glass or plastic. Total CO2 concentrations in plasma were measured with a biochemistry analyzer. Data were analyzed via repeated-measures ANOVA and multivariate regression.
Results—The air volume-to-blood volume ratio was significantly higher and consequently, plasma total CO2 concentration was significantly lower when blood was collected into 2-mL glass tubes and 2- or 3-mL plastic tubes than when the other 5 types of evacuated tubes were used. Concentrations in the other tube types were statistically equivalent. A linear relationship was detected between total CO2 concentration and air volume–to–blood volume ratio.
Conclusions and Clinical Relevance—Blood samples should be collected into evacuated tubes with a small air volume–to–blood volume ratio whenever an accurate estimate of plasma total CO2 concentration is required.
