Patent ID: 6899666

Claim:
A method for centrifugally separating whole blood into red blood cells, plasma, and a platelet concentrate, the method comprising the steps of rotating a first rotating separation zone about a rotational axis, the first rotating separation zone having radially spaced apart walls with a high-G side and a low-G side located closer to the rotational axis than the high-G side, a blood flow path that extends circumferentially about the rotation axis, the fist rotating separation zone including an entry region where whole blood enters the first rotating separation zone to begin separation and a terminal wall that is circumferentially spaced from the entry region, where separation is halted, directing whole blood into the first rotating separation zone through a first path adjacent the entry region, to begin separation of the whole blood into red blood cells toward the high-G side and plasma constituent carrying platelets toward the low-G side, directing red blood cells separated in the first rotating separation zone in a first circumferential flow direction toward the terminal wall, halting blood flow in the first circumferential flow direction at the terminal wall, successively increasing surface hematocrit in the first rotating separation zone in the first circumferential flow direction by separating the plasma constituent from the red blood cells, directing separated red blood cells from the first rotating separation zone through a second path adjacent the terminal wall, where the surface hematocrit in the first rotating separation zone is the most, directing plasma constituent separated in the first rotating separation zone in a second circumferential flow direction opposite to the first circumferential flow direction toward a different region in the first rotating separation zone that is circumferentially spaced away from the terminal wall, where the surface hematocrit in the first rotating separation zone is the least, and then directing the plasma constituent in the different region into a second rotating separation zone, separating the plasma constituent into platelet concentrate and plasma in the second rotating separation zone.