Apheresis
Apheresis employs an automated cell separator that harvests a specific blood component by centrifugal force. It involves a multi-step process that includes:
- Removal of whole blood from a donor or patient
- Separation of whole blood into components such as red cells, plasma, platelets or white cells
- Retention of the specific component needed
- Return of the unneeded recombined components to the donor.
Apheresis takes 1 to 2 hours to complete. During this time the donor or patient is connected by 1 or 2 IV lines to a sterile set of collecting and infusion bags. This closed system eliminates the risks of bacterial contamination and of returning the wrong blood to the donor.
Red cells may be collected by apheresis. Two allogeneic or autologous red cell units may be removed every 16 weeks. Volume depletion is minimized with saline infusion and the procedure is limited to individuals who are larger and have higher hematocrits (>40%) than current minimum standards for whole blood donors.
Plasmapheresis involves the separation of fresh plasma from 1.0 to 1.2 L of whole blood from a single donor, depending on the donor's weight. This component is usually processed into Fresh Frozen Plasma or Cryoprecipitate. Its larger volume (usually equivalent to 2 units FFP) can be used by one patient to reduce donor exposures or can be aliquoted to benefit several patients.
Plateletpheresis is the collection of platelets from a single donor and is often called single donor platelets. Donors should not take aspirin within 36 hours of donation. Blood pumped from one arm passes through a blood cell separator centrifugation system that collects platelets and returns plasma and red cells to the donor’s other arm. Between 4000 and 5000 mL of blood are processed over 1.5 to 2 hours. A single donor platelet concentrate contains >3.0 X 1011 platelets suspended in approximately 200 mL of plasma, which is the equivalent of 6 to 8 random donor platelet concentrates. They can be stored up to 5 days at room temperature.
Because red cells and plasma are returned, a plateletpheresis donor can give more frequently than a whole blood donor; once or twice a week. This procedure is ideal for collecting platelets from special donors such as directed donor, platelet crossmatch compatible or HLA-matched.
Single donor apheresis platelets contain fewer than 5 x 106 white blood cells and are considered to be leukocyte reduced. Additional leukocyte reduction filtration is not necessary. Rh negative patients do not need Rh immune globulin after transfusion of Rh positive apheresis platelets because they contain so few red blood cells.
