The device for sampling a small quantity of blood contained in the closed tube (1) of a blood transfusion bag, in particular for carrying out an ultimate pre-transfusion control (CPU), comprises a pipette (7, 8) linked to said closed tube (1). It differs in that it has an anti-reflux valve membrane incorporated into the wall of the closed tube at the point where the latter is linked to the pipette (7, 8) and in that it further comprises a protective case (9) sealingly moulded onto the closed tube (1) around the pipette (8) and the small conduit of same (7). The protective case opens by pulling the walls of same apart, and stays on the tube in order to allow only the pipette to be gripped. The assembly is arranged in such a way that the pipette is capable of being separated manually from the closed tube (1) by a twisting motion.
