Dilutional Effect of Ethylenediaminetetraacetic Acid on Packed Cell Volume in Healthy Dogs

Packed cell volume (PCV) is commonly used to assess and monitor red blood cell count in animals, but the results can be altered if inappropriate ratios of anticoagulant/blood are used. The purpose of this study was to determine the effect of ideally filled, overfilled, and underfilled K3 ethylenediaminetetraacetic acid (EDTA) tubes with various volumes of healthy dog blood on centrifuged PCV. Six milliliters of blood was obtained from 94 blood donors each. Initial distribution was injected into two nonheparinized microhematocrit tubes. The remainder was instilled into 1.3 mL K3 EDTA spray-dried tubes as 1.5 mL, 1.3 mL, 0.75 mL, 0.5 mL, and 0.25 mL aliquots. Normality was determined using the D'agostino-Pearson method and by visual examination of histograms. Data were analyzed using a repeated-measures analysis of variance with post hoc testing using Tukey's test. There is a statistically significant decrease in the PCV between all groups with progressive underfilling of tubes (P < .0001). The closest difference is between 1.5 and 1.3 mL (P = .0138). Our study suggested that underfilling K3 EDTA tubes significantly and negatively influences the PCV in healthy dogs. Using underfilled K3 EDTA tubes result in a lower PCV compared with directly filled microhematocrit tubes without anticoagulant.