Correction of hyperviscosity by apheresis.

Therapeutic apheresis is an extracorporeal blood purification technique designed for the removal of either plasma (plasmapheresis) or cellular blood components (cytapheresis). One of the main indications for the use of apheresis is in the treatment of the hyperviscosity syndromes that can result from either the presence of abnormal plasma components, such as antibodies, immune complexes, paraproteins, and cryoglobulins, or the excessive increase in blood cells as seen in polycythemia, leukemias, and myeloproliferative diseases. Apheresis involves withdrawal of anticoagulated blood via a vascular catheter, separation of different blood components by either centrifugation or membrane filtration, removal of the undesired component, and reinfusion of the remaining components with replacement fluid into the patient. The centrifugal method can be intermittent or continuous, the latter being faster and fully automated, and is principally used in North America. The membrane filtration technique, mainly used in Europe and Japan, involves the filtration of blood by filters of different pore sizes. These are used sequentially in a process called double or cascade filtration, enabling removal of specific plasma pathogens without need for replacement fluids. In paraproteinemias, hyperviscosity syndrome is most commonly seen with Waldenström's macroglobulinemia, followed by immunoglobulin (Ig) A and IgG (3) multiple myeloma. Single plasmapheresis with one plasma volume replacement (about 3 L) usually results in a dramatic improvement in patients with macrogobulinemia because of its predominant intravascular distribution, whereas repeated plasmapheresis is necessary with other types of paraproteins. Cryofiltration apheresis using a high-capacity cryofilter is specific for the removal of cryoglobulins. In leukemias with hyperleukocytosis, there are no evidence-based guidelines for use of leukapheresis, but it is commonly initiated when white blood cells (WBC) are > 100,000/microL or even with lower counts if leukostasis symptoms are present, especially in acute myeloid leukemia. Erythrocytapheresis and plateletpheresis are mostly used in the acute management of symptomatic patients with polycythemia vera (PV), essential thrombocytosis, and sickle cell disease.