A phlebotomy needle (24) is coupled on one conduit (11) to a source of anticoagulant contained in a flexible bag (2) and on another conduit (12) to a flexible collection bag (1). The bags (1, 2) are placed in a vacuum chamber (6) within which a vacuum is created, by a hand pump (60) operated by the donor (22). A rigid plate (4) is disposed between the two bags (1, 2). The blood flow from the donor is maintained at an adequate flow level by the donor's pumping which provides a pressure differential between the blood collection bag (1) and the needle (24). The whole blood is mixed with anticoagulant in a Y-junction device (26) immediately after passing through the phlebotomy needle. The ratio of whole blood to anticoagulant is independent of the volume of whole blood collected and is fixed by the ratio of the surface areas of the bags (1, 2) in contact with the plate (4). The anticoagulant may be gravity fed from a bottle (618) if desired. In this event the chamber (6) contains solely the blood collection bag.
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