Patent ID: 7008393

Claim:
A blood washing system comprising: an endless recirculation loop, fluidly coupled to an inlet for a source of blood; a blood separator, having an entrance port, an exit port and a removed fraction port, defining a portion of the recirculation loop between the entrance and exit ports; a pump situated along the recirculation loop operable to pump blood from and through the recirculation loop; the blood separator configured to separate blood entering the entrance port into a retained fraction, which passes through the exit port, and a removed fraction, which passes through the removed fraction port, at least a portion of the retained fraction passing through the blood separator at least a second time; a replacement fluid source fluidly coupled to the recirculation loop, whereby the replacement fluid source is configured to replace at least a part of the removed fraction; and control means programmed to control the addition of replacement fluid so as to regulate hematocrit of the fluid in the recirculation loop, wherein the hematocrit is determined by measuring resistance to flow within the blood separator.