Residual platelet counts in plasma prepared for routine coagulation testing with the Beckman Coulter Power Processor

Our laboratory has recently installed a Beckman Coulter Power Processor as part of a custom solution to fully automate our routine coagulation testing process. As part of the validation for this new system, we undertook a series of studies to assess the minimum centrifugation time required to prepare platelet-poor plasma using the National Committee for Clinical Laboratory Standards (NCCLS) guideline (H21-A3) of <10 × 10⁹/L platelets. First, residual platelet counts were measured after centrifuging 1 set each of 20 randomly selected patient plasma samples for 5, 6, 7, 8, 9, and 10 minutes. Results showed that 10 minutes was the minimum centrifugation time necessary to consistently meet the NCCLS standard. The next study was designed to evaluate the effect of elevated whole blood platelet counts (300-800 × 10⁹/L), on minimum centrifugation time. The results again supported a minimum centrifugation time of 10 minutes. Additional studies were performed to determine if elevated residual platelet counts after centrifugation for 5 minutes in the Power Processor affected the results of routine coagulation tests (prothrombin time, activated partial thromboplastin time, and fibrinogen) when compared with centrifugation for 10 minutes. Results of these studies demonstrated that centrifugation of citrated whole blood samples for 5 minutes, despite residual platelet counts >10 × 10⁹/L, produce routine coagulation results equivalent to those from samples centrifuged for 10 minutes.