Apheresis is a medical procedure that involves withdrawing a person’s blood, separating it into its individual components, removing the specific part needed, and then returning the rest of the blood back to the body. This technique allows medical professionals to target and collect a single desired blood component, such as platelets or plasma. The procedure serves a dual purpose: collecting specific components for blood donation and functioning as a therapeutic treatment to remove disease-causing elements from a patient’s bloodstream. This selective process is an example of extracorporeal therapy, meaning it is performed outside the body.
How the Apheresis Process Works
The apheresis procedure operates as a closed-loop system. The patient or donor is connected to a specialized machine through a sterile intravenous line, often placed in the arm, where blood is continuously drawn. To prevent clotting as the blood moves through the machine, an anticoagulant, such as citrate, is automatically mixed with the blood upon collection.
The machine relies on physical principles to divide the blood into its distinct parts. Separation is most commonly achieved through centrifugation, where whole blood is spun at high speeds in a rotating chamber. Because blood components vary in density, the centrifugal force causes them to settle into layers. Red blood cells, being the densest, collect on the outer wall, followed by white blood cells, platelets, and finally the least dense component, plasma, toward the center.
The machine uses sensors to detect the interface between these layers, allowing the operator to selectively divert the target component into a separate collection bag. For example, the platelet-rich layer is channeled away during a platelet collection. The remaining components—including red cells, white cells, and plasma—are then re-mixed with a saline solution. This reconstituted blood is continuously returned to the donor or patient, maintaining a stable fluid volume. In specialized cases, separation may also be achieved using filtration, where components are separated based on size as they pass across a selective membrane.
Therapeutic and Donor Applications
Apheresis has two distinct applications: donor and therapeutic procedures. Donor apheresis, often called component donation, allows healthy volunteers to provide specific blood elements in larger quantities than is possible through a standard whole blood donation. This method is useful for collecting platelets, which are difficult to obtain in sufficient numbers from whole blood, or for collecting plasma that can be processed into pharmaceutical products like immunoglobulins and clotting factors.
A process known as “double red cell” apheresis permits the collection of two units of red blood cells during a single session, offering a more efficient yield than a conventional donation. Since only the targeted component is removed and the rest of the blood is returned, donors recover faster. This allows them to donate certain components, like platelets, more frequently than whole blood.
Therapeutic apheresis is performed on patients to treat diseases by removing harmful substances from the circulation. The most common form is therapeutic plasma exchange, or plasmapheresis, where the patient’s plasma containing disease-causing elements (like abnormal antibodies or immune complexes) is removed. The removed plasma is then replaced with a substitute fluid, such as albumin or donor plasma, to restore blood volume and clotting factors. This technique manages conditions like myasthenia gravis or Guillain-Barré syndrome, where the immune system attacks the body’s own tissues.
Red cell exchange is a common treatment for patients with sickle cell disease. In this procedure, the patient’s sickled red blood cells, which cause blockages and pain, are removed and replaced with transfused healthy donor red blood cells. This reduces the percentage of abnormal cells in the bloodstream, lowering the risk of severe complications like stroke or acute chest syndrome. Cytapheresis is also used therapeutically to reduce an excessively high count of a specific cell type, such as white blood cells in leukemia or platelets in certain blood disorders.
Patient Experience and Safety
Before undergoing apheresis, patients and donors are advised to hydrate well, as adequate fluid volume supports efficient blood flow. The duration of the procedure is variable, generally ranging from one to three hours depending on the component being collected or removed. The process requires establishing vascular access, typically involving two intravenous lines—one for drawing blood and one for returning components—though some modern machines use a single needle site.
Throughout the session, trained personnel closely monitor the patient, regularly checking vital signs. The most common side effects are related to the anticoagulant, typically citrate. Citrate temporarily binds to calcium in the blood as it flows through the machine. This reduction in ionized calcium can lead to mild, temporary symptoms such as a tingling sensation around the mouth or fingertips, known as paresthesia.
Other minor side effects include lightheadedness, a slight chill, or nausea. These effects are generally mild and transient, often managed by slowing the processing rate or administering oral calcium supplements. Serious adverse events are rare. The procedure is considered safe due to continuous oversight and the technology’s built-in safety features, which include pressure sensors and air bubble detectors.