Apheresis

What is Apheresis?

Apheresis is the process of extracting blood components from the peripheral blood with the help of an apheresis machine. This machine is a centrifuge that separates blood into its components on the basis of weight. The machine can be used to obtain plasma (the liquid of the blood), platelets (see Blood Transfusion pamphlet), or white cells. For stem cell transplantation, white cells are collected during the apheresis procedures. A small percentage of these white cells are stem cells, which can restore bone marrow function. Stem cells are mother cells from which several different types of blood cells arise. When stem cells are infused into a patient's bloodstream, they will travel to the inside of certain bones and begin producing cells that eventually mature into red blood cells, white blood cells, and platelets.

How is Stem Cell Apheresis Done?

During apheresis, the patient or donor is connected to the apheresis machine. In the case of a donor, a needle is inserted into a vein in each arm. Blood is withdrawn from one arm, run through the machine to extract the stem cells, and all the remaining components of the blood are returned to the donor through the needle in the other arm. In the case of a patient donating their own stem cells, this process is performed using a central venous catheter, which has two lumens (two tubes within one catheter; see the Linecare pamphlet). Occasionally, the veins of a donor are so difficult to access that a temporary pheresis catheter in the chest or the groin becomes necessary.

What Are Possible Complications?

The actual apheresis process is painless. Patients may experience some lightheadedness, numbness or tingling of the nose, lips, or fingers, but these symptoms are short-lived and easily treatable. To collect sufficient stem cells, the apheresis process must be performed for at least two consecutive days, although five or more procedures may be necessary. Each apheresis procedure takes from three to four hours. Possible complications include bleeding at the needle sites, clotting in blood vessels used for collection (thrombosis), or surgical complications if a temporary apheresis catheter needs to be inserted. Since the procedure involves penetrating the skin, and open access to blood vessels, infection is always a risk.

Why Peripheral Blood Stem Cells?

There are several reasons and advantages for using peripheral blood stem cells (PBSC) instead of bone marrow for transplantation. Sometimes PBSC are used to add to the stem cells collected from a bone marrow harvest. Other times, a patient's bone marrow may be contaminated with cancerous cells; PBSC are then used in the hope that these cells are not similarly contaminated. Prior radiation to the pelvic area, or chemotherapy, can also reduce the number of stem cells available for bone marrow harvest. Also, PBSC can be collected without the use of general anesthesia, and the procedure is usually performed on an outpatient basis with little or no discomfort during, or after, the collection. Most importantly, more stem cells can often be collected from the peripheral blood than from the bone marrow. As a result, blood count recovery is faster after PBSC transplant than after bone marrow transplant. This faster recovery translates into a lower risk for the transplant and fewer complications.