Plasmapheresis or "plasma exchange" is a patient procedure involving the separation and removal of the plasma from the blood in order to remove a disease substance circulating in the plasma. The red blood cells, white blood cells, and platelets are returned to the patient, along with a prescribed replacement fluid. Simply stated, the "old plasma" is removed and replaced by the "new plasma", therefore there is a "plasma exchange". Why would plasmapheresis be needed? Some diseases create substances which circulate throughout the body in the plasma portion of the blood and when a person has those diseases he or she would want to go through the process of plasmapheresis to rid the plasma in their blood of those harmful substances.

Plasmapheresis is accomplished with a medical device called a blood cell separator, which is pictured above. Blood cell separators use a centrifuge or a membrane filter to separate plasma from cellular blood components. Blood is usually drawn from a patient's arm vein by a needle which is attached to a blood tubing set. Anticoagulant is added to the blood to keep it from clotting. The blood and anticoagulant enter the compartment of the blood cell separator where the plasma is separated from the cellular components and pumped into a collection bag. The cellular components are drawn from the compartment and a replacement fluid prescribed by the physician is added to replace the volume of plasma which is removed. The mix of cellular components and replacement fluid is returned to the patient, usually through a needle in the other arm. This entire process can be done in a continuous manner and with a closed circuit, so that the blood never leaves the extended circulatory system that the blood cell sep erator creates for the patient.