A device (2) for a body fluid bag, includes a filtering part (5) and a retransfusion part (6), the filtering part (5) having a filtering part inlet opening (7) and a filtering part outlet opening (8). The outlet opening (8) is arranged to be connected to an inlet opening of the body fluid bag, and the retransfusion part (6) has a retransfusion part inlet opening (10), being arranged to be connected to an outlet opening of the body fluid bag, and a retransfusion part outlet opening (11), wherein the filtering part (5) and said retransfusion part (6) are mechanically integrated to form a single unit. A transfusion unit (16) including such a device (2) is also disclosed.