Stem cells are collected through a process called apheresis. The stem cells are collected (“harvested”) at your children’s hospital or at the transplant center as your child’s bone marrow recovers from an intensive cycle of chemotherapy. A medication called granulocyte colony stimulating factor (G-CSF) is given to your child after the chemotherapy to further increase the number of stem cells in the blood.

When your child’s peripheral blood counts rise, blood is removed through a central venous catheter (specially equipped for apheresis) or a temporary catheter placed in a vein. For older children with large veins, the arms may be used, but usually the temporary catheter is placed in the neck or groin. This surgical procedure requires anesthesia. One side of the catheter collects blood, which then goes into a machine that filters out the stem cells. The filtered blood is returned to the body through the other side of the catheter. Each apheresis procedure takes 4 to 6 hours.

The number of sessions required is variable. Infants may need only one session, but older children usually need two or three sessions. In rare cases, it is impossible to get enough stem cells from the blood of children who have recently undergone extensive chemotherapy and/or radiation. In these rare instances, stem cells from the bone marrow are used.

Possible complications of peripheral blood stem cell apheresis include:

• Hypocalcemia (low calcium in the blood). Your child may experience muscle cramps, chills, tremors, tingling of the fingers and toes, dizziness, and occasionally chest pain. He will be closely monitored during the procedure, and IV or oral calcium supplements will be given to prevent this problem.
• Thrombocytopenia (low platelets). Sometimes platelets stick to the inside of the apheresis machine. Your child’s platelet count will be checked before and after the apheresis, and a platelet transfusion will be given if needed.
• Hypovolemia (low blood volume). This can occur at any time during the procedure and is more common in small children. Symptoms can include low blood pressure, rapid heart rate, lightheadedness, and sweating. To prevent this problem, the apheresis machine is generally “primed” with a unit of blood (from a blood donor) prior to the procedure.
• Infection. If your child develops fever, chills, or low blood pressure, blood cultures will be obtained and IV antibiotics given.

After collection, the child’s stem cells are treated and stored until they are used. Various compounds (e.g., dimethyl sulfoxide [DMSO]) are used to protect the stem cells during storage.

Most apheresis procedures are safely performed on an outpatient or short-stay basis, so you and your child can go home each evening. Some transplant centers, however, do require hospitalization throughout the procedure.