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The process of apheresis involves removal of whole blood from a patient or donor. Within an instrument that is essentially designed as a centrifuge, the components of whole blood are separated. One of the separated portions is then withdrawn and the remaining components are retransfused into the patient or donor.
The components which are separated and withdrawn include:
Plasma (plasmapheresis)
Platelets (plateletpheresis)
Leukocytes (leukapheresis)
In the diagram below, the process is illustrated. Whole blood is introduced into a chamber that is spinning, and the blood separates into components (P = plasma; PRP = platelet rich plasma; WBC = leukocytes; RBC = red blood cells) by gravity along the wall of the chamber. The component to be removed can be selected by moving the level of the aspiration device at the right. In this example, plasma is being removed.
The purpose of therapeutic apheresis is to remove a component of the blood which contributes to a disease state. Examples include:
Plasmapheresis: within the plasma are contained antibodies and antigen-antibody complexes that may contribute to the deleterious effects of autoimmune diseases. Removal of the plasma (and replacement with saline solution) will help to reduce circulating antibodies and immune complexes. In rare circumstances, excess blood proteins are present that may cause circulatory problems. Examples of these diseases include:
Waldenstrom's macroglobulinemia
Myasthenia gravis
Guillain-Barré syndrome
Hyperviscosity Syndromes
Paraproteinemia
Cryoglobulinemia
Goodpasture's syndrome
Plateletpheresis: rarely, in myeloproliferative disorders, the platelet count can be very high (thrombocytosis). Removal of platelets can help to avoid complications of thrombosis and bleeding.
Leukapheresis: in some cases of leukemia with very high white blood cell counts, removal of the excess leukocytes may help to prevent complications of thrombosis.
Stem Cell Harvesting: the small number of circulating bone marrow stem cells can be harvested to use in transplantation procedures.
The process of apheresis has become essential in providing blood components for therapy. A volunteer donor will undergo apheresis to supply specific components. The process takes a couple of hours. Examples include:
Plateletpheresis: this is the most common means for supplying HLA matched platelets to patients who have become HLA sensitized and require platelets from a single donor whose HLA type matches theirs.
Plasmapheresis: the plasma can be removed to supply blood components such as clotting factors. Donors can give plasma via this mechanism more often than they can donate whole blood.
Leukapheresis: the leukocytes (specifically the granulocytes) can be harvested from a donor to supply granulocytes to help fight infection in patients such as neonates.