The invention provides a syringe for preventing anemia resulting from withdrawal of blood from a patient for analysis, the syringe including a cylindrical tube having a nozzle at its lower end to which a needle is attachable; a piston disposed within the tube and apiston handle protruding from the upper end of hte tube; the syringe being further adapted to a be placed in a centrifuge for separating blood drawn from the patient into supernatant plasma component and a packed-cells component, and further comprising means for separating or removing at least a portion of teh plasma, thereby facilitating the injection of the packed-cells back into the patient The invention also provides a method for preventing anemia resulting from the withdrawal of blood from a patient for analysis.