Apheresis refers to the process of separating the cellular and soluble components of blood using a machine. Apheresis is often done on donors where whole blood is centrifuged to obtain individual blood components (eg, red blood cells [RBCs], platelets, plasma based on specific gravity) to use for transfusion in different patients. Apheresis may also be used therapeutically to treat various disorders (1).
Therapeutic apheresis includes plasma exchange and cytapheresis
Apheresis is generally tolerated by healthy donors. However, many minor and a few major risks exist.
Insertion of the large IV catheters necessary for apheresis can cause complications (eg, bleeding, infection, pneumothorax).
Citrate anticoagulant may decrease serum ionized calcium.
Replacement of patient's plasma with a colloidal solution (eg, 5% albumin or fresh frozen plasma does not replace IgG and coagulation factors.
Most complications can be managed with close attention to the patient and manipulation of the procedure, but some severe reactions and a few deaths have occurred.
General reference
1. Padmanabhan A, Connelly-Smith L, Aqui N, et al: Guidelines on the Use of Therapeutic Apheresis in Clinical Practice: Evidence-Based Approach from the Writing Committee of the American Society for Apheresis: The Eighth Special Issue. J Clin Apheresis 34:171–354, 2019. doi: 10.1002/jca.21705
Plasmapheresis
Plasmapheresis refers to the process of separating plasma from blood, typically by centrifugation or filtration. Plasmapheresis is often done on healthy donors to obtain plasma only, which is used for transfusion to patients or as a source for plasma derivative preparations (eg, albumin, clotting factor) derived from plasma pooled from thousands of donated units. Because donors typically give only 1 unit (about 500 mL) of plasma and must be in good health, there is no need to replace the removed plasma.
Plasmapheresis also may be done therapeutically to remove certain deleterious substances (eg, autoantibodies, immune complexes) that circulate in plasma. Because large volumes of plasma must be removed, patients are transfused with plasma from healthy donors; thus, this process is termed plasma exchange.
Plasma exchange
Therapeutic plasma exchange removes plasma components from blood. A blood cell separator extracts the patient’s plasma and returns RBCs and platelets in plasma or a plasma-replacing fluid; for this purpose, 5% albumin is preferred to fresh frozen plasma (except for patients with thrombotic thrombocytopenic purpura) because it causes fewer reactions and transmits no infections. Therapeutic plasma exchange resembles dialysis but, in addition, can remove protein-bound toxic substances. A one-volume exchange removes about 65% of such components.
To be of benefit, plasma exchange should be used for diseases in which the plasma contains a known pathogenic substance, and plasma exchange should remove this substance more rapidly than the body produces it. For example, in rapidly progressive autoimmune disorders, plasma exchange may be used to remove existing harmful plasma components (eg, cryoglobulins, antiglomerular basement membrane antibodies) while immunosuppressive or cytotoxic drugs suppress their future production.
There are numerous, complex indications. Clinicians typically follow Guidelines on the Use of Therapeutic Apheresis from the American Society for Apheresis (1). The frequency of plasma exchange, the volume to be removed, the replacement fluid, and other variables are individualized.
Low density lipoprotein (LDL) cholesterol can be selectively removed from plasma by adsorption over a column (called LDL apheresis).
In photopheresis, mononuclear cells are selectively removed by centrifugation and treated with photoactivatible drugs (eg, 8-methoxypsoralen) that are then activated with ultraviolet light; it is a form of immunomodulatory therapy.
In immunoadsorption, an antibody or antigen is removed from plasma by combining with an antigen or antibody chosen to bind the target antibody or antigen over a column.
Complications of plasma exchange are similar to those of therapeutic cytapheresis.
Cytapheresis
In cytapheresis, the cellular components of blood (eg, RBCs, white blood cells [WBCs], platelets) are separated. This is often done on donated blood so that each component may be given to a different recipient. Cytapheresis also may be done therapeutically to remove excess or defective cellular components.
Therapeutic cytapheresis
Therapeutic cytapheresis removes cellular components from blood, returning plasma.
It is most often used to remove defective RBCs and substitute normal ones in patients with sickle cell disease who have the following conditions: acute chest syndrome, stroke, pregnancy, or frequent, severe sickle cell crises. RBC exchange achieves hemoglobin S levels of < 30% without the risk of increased viscosity that can occur because of increased hematocrit with simple transfusion.
Therapeutic cytapheresis may also be used to reduce severe thrombocytosis or leukocytosis (cytoreduction) in acute leukemia or in accelerated or blast crisis phase of chronic myeloid leukemia when there is risk of hemorrhage, thrombosis, or pulmonary or cerebral complications of extreme leukocytosis (leukostasis).
Therapeutic platelet removal (plateletpheresis) is effective in essential thrombocythemia because platelets are not replaced as rapidly as white blood cells. One or two procedures may reduce platelet counts to a lower level, but the effect is temporary and the platelet count is not restored to normal.
Therapeutic WBC removal (leukapheresis) can remove kilograms of buffy coat in a few procedures, and it often relieves leukostasis. However, the reduction in WBC count itself may be mild and only temporary.
Other uses of cytapheresis include collection of peripheral blood stem cells for autologous or allogeneic bone marrow reconstitution (an alternative to bone marrow transplantation) and collection of lymphocytes for use in immune modulation cancer therapy (adoptive immunotherapy).