Platelet counting using plasma platelet concentrate samples

Platelet counting using samples of plasma from platelet concentrates prepared for transfusion was assessed. The methods employed included a manual phase-contrast method, and counting with Coulter S Plus and Sysmex E-2500 counters. All methods were reproducible (mean CV of 4.9, 2.2 and 1.4%, respectively). However, neat samples of platelet concentrates analysed by Coulter counter were inaccurate (mean count of 863.8 x 10(9)/l compared to 1018.9 x 10(9)/l counted manually). Moreover, the Coulter platelet counts were non-linear above 900 x 10(9)/l, whereas the E-2500 platelet counts were linear to 2700 x 10(9)/l. A one-in-three pre-dilution was required to obtain accurate, linear counts with the Coulter counter, whereas the E-2500 was accurate without pre-dilution (mean count of 1030.2 x 10(9)/l compared to 1018.9 x 10(9)/l counted manually). In conclusion, the method of platelet counting may affect true platelet yields.