Apheresis is a medical technology that separates whole blood into its individual components (such as red cells, plasma, and platelets) for donation or therapeutic treatment. The procedure involves temporarily removing blood, processing it through specialized equipment to isolate a specific component, and then returning the rest of the blood to the body. The duration varies significantly based on whether the goal is standard donation or complex medical therapy.
Defining Apheresis and Its Core Mechanism
The fundamental mechanism of apheresis involves a continuous, automated cycle of blood withdrawal, separation, and return. Blood is drawn from the patient or donor, typically through a needle in a vein, and guided into the apheresis machine where it is separated into its constituent parts using physical principles.
The most common separation method is differential centrifugation, where blood is spun at high speed, allowing components to settle into distinct layers based on density and size. Alternatively, some devices use membrane filtration, passing the blood through specialized filters. Once the targeted component (plasma, platelets, or stem cells) is isolated, it is collected in a sterile bag. The remaining blood elements are mixed with an anticoagulant and returned to the person.
Standard Donor Procedures: Typical Durations
The duration of donor apheresis procedures is predictable and depends on the blood component collected. These procedures are the most common type encountered by the general public. The longest routine donation is platelet collection (plateletpheresis), which usually takes between 90 and 120 minutes of machine time to gather a sufficient quantity of platelets.
Plasma donation (plasmapheresis) is a shorter process, generally lasting 45 to 60 minutes. Since plasma is the liquid portion of the blood and is quickly replaced, the machine processes the required volume faster than collecting platelets. Double red cell donation collects two units of red blood cells instead of one unit of whole blood. Machine time for this specialized donation is usually around 25 to 45 minutes. These estimates refer only to the actual connection time, not the total time spent at the donation center, which includes screening and recovery.
Therapeutic and Specialized Procedures: Longer Timelines
Apheresis procedures used as medical treatments often require significantly longer durations due to the nature of the condition. Therapeutic Plasma Exchange (TPE), for example, involves removing the patient’s plasma, which contains disease-causing substances like abnormal antibodies, and replacing it with a substitute fluid. A single TPE session typically lasts between two and four hours, necessary to process one to one-and-a-half times the patient’s total plasma volume to effectively reduce harmful components.
The longest procedures involve the collection of hematopoietic stem cells, performed to prepare a patient for a bone marrow transplant or to collect cells from a healthy donor. Since stem cells are present in very low concentrations in circulating blood, the machine must process a large volume to harvest the required dose. A stem cell collection session can last anywhere from three to eight hours. Patients or donors may need to undergo the procedure for one to three consecutive days to ensure enough cells are collected for a successful transplant.
Variables That Extend or Shorten the Procedure
Several physiological and logistical factors, beyond the component collected, influence the final duration of an apheresis procedure. The quality of the patient’s or donor’s venous access is a major determinant of how quickly the blood can be drawn and returned. If veins are small or difficult to access, a slower blood flow rate must be set on the machine, which automatically extends the total collection time.
The patient’s hydration status also plays a role; being well-hydrated contributes to better blood flow and helps the body tolerate the procedure more effectively. The use of anticoagulants, like sodium citrate, can sometimes cause a temporary drop in blood calcium levels. If a person experiences symptoms like tingling or muscle cramps, the machine’s processing rate may need to be slowed down to manage this reaction, adding time to the overall process.
Therapeutic Variables
For therapeutic procedures, the machine’s collection efficiency and the concentration of the target substance in the blood are key variables. For example, the pre-procedure circulating CD34+ cell count for stem cell harvests determines the necessary processing volume and, consequently, the final duration.