Bone marrow donation (BMD) is a lifesaving treatment for patients with blood cancers and other diseases, but the term itself can be misleading about the amount collected. The procedure is not a one-size-fits-all process; the material harvested is precisely calculated based on the recipient’s medical requirements. Modern BMD primarily involves two distinct methods: Peripheral Blood Stem Cell (PBSC) donation and the less common surgical Bone Marrow Aspiration. The specific volume of product collected is determined entirely by the need for a sufficient dose of blood-forming cells, which dictates the length and type of the donation process.
How the Target Amount is Calculated
The goal of a stem cell donation is to obtain a precise number of hematopoietic stem cells (HSCs) necessary for the recipient’s recovery, rather than collecting a specific volume of liquid. These cells are identified by a specific surface marker, known as CD34+, which makes them measurable. The target amount is quantified in terms of a minimum cell dose per unit of the recipient’s body weight.
The fundamental calculation involves multiplying the required minimum cell dose by the recipient’s body weight, typically measured in kilograms. A common minimum target for successful engraftment is at least 2 million CD34+ cells per kilogram of the recipient’s weight. The transplant team may aim for 3 to 5 million cells per kilogram to provide a safety margin or collect enough for a potential second transplant.
This required cell dose is influenced by several factors, including the severity of the patient’s disease, their prior treatments, and the type of transplant. Once the target cell count is established, the collection procedures are performed until this number is met, regardless of the volume of liquid collected.
The Volume Collected During Peripheral Blood Stem Cell Donation
Peripheral Blood Stem Cell (PBSC) donation is the most common method, accounting for approximately 90% of all stem cell collections. This non-surgical method involves a process called apheresis, which is similar to donating platelets. Before the donation, the donor receives daily injections of granulocyte colony-stimulating factor (G-CSF) for several days. This stimulates the stem cells to move from the bone marrow into the circulating bloodstream.
During the apheresis procedure, blood is continuously drawn from one arm and passed through a specialized machine. The machine spins the blood to separate the components, isolating the stem cells and collecting them into a sterile bag. The rest of the blood components are safely returned to the donor through the other arm. The procedure typically lasts about four to six hours.
The volume of blood processed through the machine can be significant, often ranging from 10 to 20 liters cycled over the course of the procedure. However, the volume of the final product collected is very small and highly concentrated. This concentrated stem cell product is generally only about 150 to 250 milliliters, which is less than the volume of a standard soda can. If the target cell count is not met in one session, the donor may need to return for a second collection the following day.
The Volume Collected During Bone Marrow Aspiration
Traditional bone marrow aspiration is a less frequent method involving the collection of liquid marrow from the bone. This procedure is surgical, performed in an operating room, and requires the donor to be under general or regional anesthesia. The donation involves using a hollow needle to repeatedly withdraw liquid marrow from the posterior iliac crest (the back of the pelvic bone).
The total volume of the liquid mixture collected is calculated based on the recipient’s required cell dose and the donor’s body weight. The collected product is a mixture of actual marrow and peripheral blood. The typical range for this mixture is between 1 to 1.5 liters, which is slightly more than the volume of a large bottle of soda. This volume represents approximately 2% to 5% of the donor’s total marrow, which their body naturally replaces over the next few weeks.
Because a significant volume of fluid containing blood is removed, donation standards limit the total amount collected to no more than 20 milliliters of marrow per kilogram of the donor’s weight. To compensate for the fluid loss, the donor is often given intravenous fluids. If the collected volume is at the higher end of the range, the donor may occasionally receive a blood transfusion, sometimes using their own pre-donated blood.