Platelet concentrations and platelet-associated IgG in greyhounds

Background: Greyhounds have lower platelet concentrations (PC) than dogs of other breeds have. No underlying cause has been investigated. Hypothesis: We hypothesized that Greyhounds have lower mean PC because of breed variation, not immune-mediated causes. Our secondary hypothesis was that PC is dependent on the method of analysis. Animals: Sixty privately owned Greyhounds in Kansas. Methods: Blood samples were collected into evacuated glass tubes containing ethylenediamine tetraacetic acid (EDTA). Blood smears were evaluated for platelet clumps. All 60 samples had PC determined by manual, impedance, and buffy coat analyzer methods. Results of the 60 samples were compared with results of samples with (n = 25) and without (n = 35) clumps, and with control dogs. Platelets were assayed for the presence of surface-associated antigen (PSAIgG) by direct immunofluorescence. Results: The mean PC was below that of the control dogs for the impedance method (P < .001). No significant difference in PC was detected between analysis methods or between samples with or without platelet clumps. Three of 60 (5%) of the Greyhounds had PC between 50,000 and 100,000/μL with impedance analysis; no samples had <100,000/μL via buffy coat analysis. PSAIgG was not identified in any samples. Conclusions and Clinical Importance: The mean Greyhound PC for the impedance method was below the reference interval for control dogs but was not significantly different from PC determined by other methods. An immune-mediated cause for the lower PC was unlikely because no samples had PSAIgG. The decreased PC is most consistent with breed variation. As only 0-5% of samples, depending on analysis method, had PC <100,000/μL, a Greyhound with a PC <100,000/μL is not necessarily consistent with breed variation, thus diagnostic testing is indicated.