Reducing white cells in platelet units.

White cells (WBCs) constitute a significant contaminant of platelet concentrates (PCs). Various technologies, including apheresis and filtration, are currently being developed to minimize the carryover of WBCs into platelets. The aim is to reduce contamination of less than 10(8) WBCs per platelet unit. As part of quality control monitoring of the blood bank operations, the centrifugation protocols employed in the preparation of platelet-rich plasma (PRP) have been evaluated for their impact on the WBC content of the PCs. The WBC content, which is expressed throughout the PRP volume as well as in the PC, reflects the degree of braking. For example, after centrifugation (2500 rpm, 4 min) of whole blood into packed red cells (RBCs) and PRP, braking-induced mixing increases the WBC content of the expressed PRP. Variations in the braking rates of the centrifuges used also correlate with the WBC carryover into packed platelets. An alternative centrifugation protocol to minimize WBC carryover is suggested. Whole blood is centrifuged at 2500 rpm for 1.5 minutes (rather than 4 min) and allowed to stop with no braking. This procedure adds some 3 minutes to the total centrifugation time, but the relative integral of this centrifugation program is approximately 50 percent smaller than that of the normally employed centrifugation protocol (with braking). It was observed that the WBC content throughout the expressed PRP, or in the entire PC, is reduced by about 75 percent. These results show that an effective method of significantly decreasing the WBC content of platelet units is simply to prepare PRP with reduced centrifugation time and with the braking programs disengaged.