Plasmapheresis
Apheresis is the process of removing whole blood from a patient or blood donor, separating the components of the blood (usually by centrifugation), and returning only selected components to the original patient or donor.
The process is illustrated in the diagram (right). Whole blood enters the centrifuge (spinning chamber) at the right and separates into components according to their mass (heaviest at the bottom) under gravity. The component to be removed can be altered by raising or lowering the aspiration device on the right. In this case, blood plasma is being removed.
Types of apheresis
Apheresis can be subdivided into different types, depending on which component of blood is being removed.
Theraputic apheresis
Theraputic apheresis is conducted to remove a portion of the blood which contributes to a disease.
Plasmapheresis
Suspended in the plasma are antibodies and immune complexes that may contribute to the effects of autoimmune disease. Removal of the plasma and its replacement with isotonic saline solution will help to reduce these circulating components and thus may dampen the symptoms of the disease. In rare circumstances there may be an excess of blood proteins that cause circulatory problems.
Examples of diseases that can be treated with plasmapheresis:
Plateletpheresis
In myeloproliferative disorders, the platelet count may be very high (thrombocytosis). In this case, reduction in the number of platelets can help to avoid the complications of thrombosis and bleeding.
Leukapheresis
In some cases of leukaemia with very high white blood cell counts, removal of excess leukocytes may help to avoid the complications of thrombosis.
Donation by apheresis
Apheresis is sometimes conducted during blood donation when a certain blood component, such as blood plasma or leukocytes are particularly needed. The donor will undergo apheresis to supply the specific blood components required. The process takes a couple of hours.
Plasmapheresis
Plasma contains blood components such as clotting factors, which some patients may be unable to produce themselves. Donors can give plasma in this way more often than they could give whole blood.
Plateletpheresis
Plateletpheresis is used to supply HLA matched platelets to patients who have become HLA sensitised and thus require platelets from a single donor whose HLA type matches their own.
Leukapheresis
Leukacytes (specifically granulocytes) can be harvested from a donor and given to a patient who needs them, for example, to help fight infection in a newborn baby.
