Evaluation of techniques for counting bovine platelets.

Visual and electronic techniques for counting bovine platelets were investigated. The reference method used was hemacytometer counting of platelets in whole blood diluted with 0.85% NaCl solution. A whole blood platelet-rich plasma technique was imprecise and inaccurate. Isopycnic centrifugation of blood diluted in 8.01% NaCl solution (same density as platelets) was a precise technique, but the whole blood platelet count was underestimated. The most precise and accurate technique investigated was unit gravity sedimentation of a 1:100 dilution of blood with 10 ml of Isoton followed by electronic counting of platelets in the supernatant. This technique correlated very well with visual counting of bovine platelets (N = 77, y = 55 + 0.80x, r = 0.89, P less than 0.01).