EFFECTS OF SAMPLE HANDLING ON TOTAL CARBON-DIOXIDE CONCENTRATIONS IN CANINE AND FELINE SERUM AND BLOOD

Objective-To determine whether underfilling blood collection tubes lea ds to in vitro reduction in serum measured total CO2 concentration ([T CO2](m)) in canine and feline blood samples sufficient to create the i mpression of metabolic acidosis (pseudometabolic acidosis) or high ani on gap. Sample Population-Blood samples from healthy client-owned anim als (16 dogs, 17 cats). Procedure-Venous blood samples were collected in random order for determination of serum [TCO,] and blood gas tensio ns. Blood gas analysis was performed on iced, capped blood samples. In dogs, serum [TCO2] was measured in 1-, 3-, and 10-ml samples in 10-ml type-B tubes and in a 3-ml sample in 3-ml type-A tubes. In cats, seru m [TCO2] was determined in 1-, 2-, and 3-ml samples in 3-ml type-A tub es and in a 3-ml sample in 10-ml type-B tubes. Results-For dogs, serum [TCO2] in full-tube, 10-ml samples was a mean +/- SD, 2.0 +/- 1.1 mmo l/L greater than that in 3-ml samples and 3.7 +/- 1.3 mmol/L greater t han the value in 1-ml samples, both differences were significant at P < 0.0001. The serum [TCO2] in full 3-ml samples was lower by 0.4 +/- 0 .6 mmol/L than the value in full-tube 10-ml samples (P = 0.019). For c ats, serum [TCO2] in full-tube, 3-ml samples was 0.5 +/- 0.6 mmol/L gr eater than that in 2-ml samples (P = 0.004) and was 1.5 +/- 0.8 mmol/L greater than the value in 1-ml samples (P < 0.0001). Serum [TCO2] in 3-ml samples of feline blood in 10-ml tubes was 0.8 +/- 0.8 mmol/L low er than that in samples from full 3-ml tubes (P = 0.0007). In dogs and cats, [TCO2] in fully filled collection tubes was approximately 6 mmo l/L higher when calculated from blood gas analysis data than when chem ically determined in serum. Conclusions and Clinical Relevance-Underfi lling blood collection tubes results in a false decrease in serum [TCO 2], which can contribute in part to descrepancies between blood gas an d chemical analyses as estimates of plasma bicarbonate concentration. This, and other in vitro effects of sample handling and collection, ma y result in a false assessment of metabolic acidosis in dogs and cats.