Apheresis apparatus for separating an intermediate density component from whole blood

Apparatus for separating an intermediate density component from whole blood, the intermediate density component consisting primarily of at least one of a platelet constituent and a white blood cell constituent, the apparatus comprising:

• a centrifuge having a fractionation volume, for separating whole blood into blood components, each of which has a density, so that each of the blood components occupies a region having a radial position in the fractionation volume according to the density of the blood component, the blood components including a lower density component and higher density components including the intermediate density component;
• an inlet port, through which whole blood enters the centrifuge, and an outlet port, through which fluid exits the centrifuge, mounted on said centrifuge, the ports being in fluid communication with said fractionation volume;
• a first container in selective fluid communication with said ports for collecting the lower density component exiting said outlet port;
• a first pump, coupled to the first container and the inlet port, for delivering lower density component front the first container to the inlet port;
• means for operating the first pump to recirculate lower density component front the first container through the inlet port into the fractionation volume
• (a) at a first, substantially constant, rate so as to widen the region occupied by the intermediate density component without causing said intermediate density component to exit the fractionation volume, and subsequently
• (b) at a second rate, so as to displace intermediate density component from the fractionation volume out the outlet port.