Comparison of manual and automated methods for determining platelet counts in dogs with macrothrombocytopenia

Department of Anatomy and Physiology, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark.

Platelet counts were performed in 43 Cavalier King Charles Spaniels (CKCS, a breed predisposed to macrothrombocytopenia) and in 10 control dogs using 3 automated systems and 3 manual methods (erythrocyte-lysing agents + counting chamber or evaluation of blood smear). Good correlations were found between platelet counts using all methods (all P < 0.0001; R2 = 0.71-0.85). Best correlations were found between the manual methods. Significantly larger platelets were found in CKCS with platelet count < or = 100,000/microl when compared with control dogs and CKCS with platelet count > 100,000/microl (both P < 0.0001). All platelet counts--except when made with the 2 counting chamber methods--were underestimated at platelet counts < or = 100,000/microl.