Abstract: An apheresis apparatus for increasing the purity and yield of platelets separated from donated whole blood by centrifugation incorporates a centrifuge for separating whole blood into lower, intermediate, and higher density components. The centrifuge has inlet and outlet ports in selective fluid communication with a container for receiving lower density blood component from the outlet port. A pump is coupled to the container and the inlet port for recirculating lower density blood component from the first container through the inlet port into the centrifuge at a first, substantially constant, rate so as to widen the region of the centrifuge occupied by the intermediate density component without causing the intermediate density component to exit the centrifuge, and subsequently at a second rate, so as to displace intermediate density component from the centrifuge.

Abstract: An apheresis apparatus and method is disclosed for increasing the purity and yield of platelets separated from donated whole blood in a centrifuge. The whole blood in the centrifuge is diluted by recirculating fluid, such as plasma or saline, at a first flow rate, to mix with further withdrawn whole blood prior to entering the centrifuge. As plasma is collected, it is recirculated through the centrifuge at a second flow rate to further improve the separation between the intermediate density components, i.e., platelets and white blood cells in the "buffy coat." The plasma is then recirculated through the centrifuge at a third flow rate and platelets are displaced out of the centrifuge while the plasma is recirculating through the centrifuge at the third flow rate.