Therapeutic apheresis is a specialized medical process that involves temporarily removing a patient’s whole blood, separating it into its components, treating or removing a specific problematic part, and then returning the remaining, treated components back into the bloodstream. This procedure is distinct from a standard blood donation, which collects components from a healthy volunteer for transfusion. In therapeutic apheresis, the immediate goal is to treat a disease by directly filtering the patient’s blood outside of the body to remove disease-causing substances.
Defining Therapeutic Apheresis
Therapeutic apheresis is an extracorporeal treatment designed to remove a component of blood that is causing or contributing to a medical condition. The process generally follows a three-step cycle: whole blood is withdrawn from the patient, separated into its various parts by a specialized machine, and the targeted problematic component is removed while the rest of the blood is returned to the patient. This method is employed when a disease is driven by a substance circulating in the blood that can be efficiently removed.
This procedure is broadly categorized into two major types based on the blood component targeted for removal. Plasmapheresis involves the separation and removal of the liquid portion of the blood, known as plasma, which often contains harmful antibodies or proteins. The second main category is cytapheresis, which focuses on removing specific cellular components, such as excess or damaged red blood cells, white blood cells, or platelets.
In plasmapheresis, the removed diseased plasma is typically replaced with a substitute fluid, such as a solution of human albumin or fresh frozen plasma, before the blood is returned. This replacement ensures the patient’s fluid volume is maintained and the blood’s normal balance is restored, completing the therapeutic exchange.
The Mechanics of Blood Component Separation
The separation of blood components is achieved through two primary methods, each relying on different physical principles. The first and most common method is centrifugation, which uses rapid spinning to separate the blood’s elements based on their density. Whole blood is continuously drawn into a spinning chamber within the machine, creating an artificial gravitational field.
Red blood cells, the densest components, are forced to the outermost wall of the chamber. Progressively less dense layers form inward: white blood cells and platelets settle next, and the least dense component, the plasma, collects in the center. The machine uses precisely positioned ports to skim off the targeted layer, whether it is plasma for an exchange or a specific cellular layer for cytapheresis. Centrifugation is highly versatile and is the only method capable of selectively removing specific cellular components.
The second separation method is membrane filtration, which uses a semi-permeable filter to separate plasma based on molecular size. In this technique, whole blood passes across a filter membrane with microscopic pores large enough to allow the liquid plasma, along with its dissolved proteins and antibodies, to pass through.
The pores are too small for the cellular components—red cells, white cells, and platelets—to cross, effectively leaving them behind. This method is primarily used for plasmapheresis, as it allows for the bulk removal of plasma while the cells are immediately redirected for return to the patient.
Conditions Treated by Apheresis
Therapeutic apheresis is used to treat diseases where the illness is mediated by a circulating substance in the blood. Plasmapheresis is frequently employed to manage acute exacerbations of various autoimmune and neurological disorders. For conditions like Guillain-Barré Syndrome and Myasthenia Gravis, the body mistakenly produces autoantibodies that attack the nervous system.
Plasmapheresis rapidly removes these harmful antibodies from the plasma, providing immediate clinical relief that can stabilize the patient while long-term immunosuppressive therapies take effect. The procedure is often combined with medication to suppress the immune system and prevent the body from quickly producing new autoantibodies. Plasmapheresis is also a standard treatment for Thrombotic Thrombocytopenic Purpura (TTP), a rare blood disorder involving abnormal clotting.
Cytapheresis, particularly red blood cell exchange, is a fundamental therapy for managing severe complications of Sickle Cell Disease (SCD). Patients with SCD have red blood cells containing abnormal hemoglobin S (HbS) that can deform and block blood vessels. The red cell exchange procedure removes the patient’s sickle-shaped red blood cells and replaces them with healthy donor red blood cells containing normal hemoglobin A (HbA).
This isovolemic exchange efficiently reduces the percentage of HbS in the blood to a safer level, typically below 30%, which significantly lowers the risk of stroke and acute chest syndrome. Unlike simple blood transfusions, the exchange maintains the patient’s total blood volume and prevents the hyperviscosity and iron overload that can result from repeatedly adding new red cells without removing the old ones. Another form of cytapheresis, leukapheresis, is used as an emergency treatment to rapidly reduce dangerously high white blood cell counts in patients with certain types of leukemia.
Patient Preparation and Procedure Logistics
Before undergoing therapeutic apheresis, patients are instructed to hydrate thoroughly to ensure adequate blood flow and reduce the risk of lightheadedness. Pre-procedure testing confirms blood counts and ensures the availability of appropriate replacement fluids, such as human albumin solution. A successful procedure relies on having reliable vascular access to circulate the patient’s blood into and out of the machine.
Vascular Access
For the majority of patients requiring only a few treatments, peripheral venous access (PVA) in the arms is sufficient, often utilizing two large-bore needles or a single-needle cycling technique. If the patient has poor peripheral veins or requires a chronic, long-term treatment plan, a temporary central venous catheter (CVC) or a surgically placed permanent access, such as an arteriovenous fistula, may be necessary. The machine requires a steady flow of blood, typically between 50 and 100 milliliters per minute, to operate effectively.
The procedure itself usually lasts between two and four hours, depending on the patient’s blood volume and the amount of plasma or cells that need to be processed. Patients are monitored closely throughout the session for potential physical reactions. The most common reactions are temporary lightheadedness or a tingling sensation caused by the anticoagulant used in the machine circuit.