Effect of anticoagulant and storage conditions on platelet size and clumping in healthy dogs

The potential impact of preanalytical factors, such as type of anticoagulant, storage temperature, and time, on the formation of macroplatelets and platelet aggregates (platelet clumping) in dogs is largely elusive. The objective of the current study was to assess the effect of anticoagulant, temperature, and blood storage time in the light microscopy-generated macro platelet percentages and the frequency of visually inspected platelet aggregates in clinically healthy dogs. Giemsa-stained blood smears from 70 healthy dogs were reviewed after exposure to different anticoagulants (ethylenediamine tetra-acetic acid [EDTA] vs. citrate), temperatures (25 degrees C vs. 4 degrees C), and storage times (up to 24 hr postsampling). The mean percentage of macroplatelets (platelets with diameter or length :5 pin) was higher (P = 0.0006) when EDTA was used as the anticoagulant. For either anticoagulant, the mean percentage of macroplatelets was higher (P < 0.0001) at 25 degrees C than at 4 degrees C. Platelet clumping was 1.9 times (P < 0.0001) more likely to occur when citrate- rather than EDTA-anticoagulated blood was examined; regardless of the anticoagulant used, clumping occurred 3 times (P < 0.0001) more often when samples were preserved at 4 degrees C than when they were preserved at 25 degrees C. Storage time did not significantly influence the macroplatelet percentages or the frequency of platelet clumping. The results of this study indicate that macroplatelet percentages in the canine blood should be interpreted in relation to anticoagulant- and temperature-specific reference intervals and that future studies are Warranted in order to investigate the clinical relevance of this calculation. In addition, the significant association of citrate with the formation of platelet aggregates may preclude its use for platelet enumeration in the dog.