Platelet concentration and platelet volume distribution in healthy cats

An electronic particle counter and size analysis system were used to determine platelet count, mean platelet volume (MPV), platelet volume heterogeneity (SD of platelet volumes), and platelet mass values in feline platelet-rich plasma (PRP) prepared by brief centrifugation of blood. Electronic platelet counts correlated well with manual counts done by phase microscopy over a platelet count range of 5,000/microliters to 840,000/microliters (r = 0.93). Variability in manual and electronic counts was not significantly different. However, due to differential stratification of platelet concentration in PRP, electronic counts on aspirated, mixed PRP were significantly less variable (P less than 0.01). Reference values, determined on blood from 25 healthy adult cats, were platelet count: 296,000 to 850,000/microliters; MPV: 11.0 to 18.1 fl; platelet volume heterogeneity: 5.8 to 10.6 fl, and platelet mass: 4.0 to 11.4 microliters/ml of blood. There was a direct relationship between MPV and platelet volume heterogeneity and an inverse relationship between MPV and platelet count. Platelet concentration and size were not constant in different PRP layers. Aliquots of PRP near the top had a significantly lower platelet concentration (P less than 0.001) and lower MPV (P less than 0.001) than did aliquots from near the bottom of the PRP layer. During the 4 hours after sample collection, there was a progressive decrease in platelet count and progressive increase in MPV, but the changes were not significant. When platelets were incubated in counting fluid, there was a slight increase in MPV by 1.5 hours. By 2.5 hours, there was a significant increase in MPV (P less than 0.05).