In a surgical bone marrow donation, doctors usually collect about one liter or less of liquid marrow mixed with blood, which is only a small fraction of the marrow in your body. The exact amount depends on the recipient’s body weight and on a safety limit based on your own weight. Your body replaces the donated marrow cells within a few weeks, which is why donation does not weaken your immune system or blood production in the long run.
What Bone Marrow Is and Why Patients Need It
Bone marrow is the soft, spongy tissue inside large bones such as the pelvis, spine, and breastbone. It contains hematopoietic stem cells, the parent cells that produce every red cell, white cell, and platelet through a process called hematopoiesis. Our article on the composition and function of bone marrow explains this in more detail.
A transplant of healthy donor stem cells can rebuild blood production in patients whose own marrow is diseased or destroyed. People who may need one include those with leukemia, lymphoma, myelodysplastic syndromes, inherited bone marrow disorders, and severe aplastic anemia. These sit within the wider group of blood disorders that transplant teams treat.
How Much Bone Marrow Can You Donate?
The volume collected during a bone marrow harvest is calculated for each transplant. Two numbers drive it:
- The recipient’s needs. Transplant teams aim for a target number of stem cells per kilogram of the recipient’s weight, so a large adult recipient needs more than a small child.
- The donor’s safety limit. Harvest centers commonly cap collection at around 20 milliliters per kilogram of the donor’s body weight, so a smaller donor gives less.
In practice, adult harvests typically fall somewhere between about 500 milliliters and 1.5 liters of marrow-blood mixture, with around one liter being common. Much of that liquid is actually blood, because marrow is drawn out through a needle and blood comes with it.
| Measure | Typical figure |
|---|---|
| Volume collected (adult donor) | About 0.5 to 1.5 liters of marrow and blood |
| Common donor safety cap | Around 20 mL per kg of donor weight |
| Share of total marrow removed | A small fraction, often quoted as a few percent |
| Time for marrow cells to regrow | A few weeks |
| Time for red cell levels to fully recover | Several weeks |
The key point for donors is that marrow is spread through many bones, and what is taken from the back of the pelvis is a small portion of the whole. Your stem cells quickly replace the cells removed.
Two Ways to Donate: Marrow Harvest vs PBSC
There are two ways to give stem cells, and the transplant doctor asks for the one that suits the patient best. Our guide to donating bone marrow covers the full process.
Bone Marrow Harvest
This is a surgical procedure done under general or regional anesthesia. With the donor lying face down, the doctor uses a hollow needle to draw marrow from the back of both hip bones through several small punctures in the skin. There are no stitches or large cuts. The procedure usually takes one to two hours, and many donors go home the same day or the next morning.
Peripheral Blood Stem Cell (PBSC) Donation
In PBSC donation, the donor receives daily injections of a growth factor called filgrastim for about four to five days. This pushes stem cells out of the marrow into the bloodstream. They are then collected by apheresis, where blood runs from one arm through a machine that separates stem cells and returns the rest through the other arm. A session takes several hours and occasionally a second day is needed.
| Feature | Marrow harvest | PBSC donation |
|---|---|---|
| Anesthesia | Yes | No |
| Where cells come from | Back of the pelvic bones | Bloodstream, via apheresis |
| Common side effects | Lower back or hip soreness, tiredness | Bone aches and headache from the injections |
| Typical return to normal | About one to two weeks for most activities | Usually within a few days |
Safety, Screening, and Side Effects
Every potential donor has a medical assessment before donation. This includes a health history, physical examination, complete blood count, metabolic and infection tests, and for marrow harvest, a check that anesthesia is safe. If anything suggests donation could harm you, it does not go ahead.
After a marrow harvest, the most common effects are soreness over the hip bones, back pain, fatigue, and a temporarily lower blood count. Some centers collect a unit of the donor’s own blood beforehand to give back if needed. Serious complications are rare and mostly relate to anesthesia.
Donors should contact the collection center if they notice fever, redness or discharge at the puncture sites, severe pain, or unusual breathlessness. Most people are back at desk work within a few days.
Matching and What Happens for the Recipient
Donors are matched to patients by human leukocyte antigen (HLA) typing, a set of immune markers on cells. A close HLA match lowers the risk of rejection and of graft-versus-host disease (GVHD), where donor immune cells attack the patient’s body.
The recipient first receives conditioning chemotherapy, sometimes with radiation, to clear their diseased marrow. The donated cells are then given through a drip, much like a blood transfusion, and travel to the recipient’s marrow to start making new blood cells. Recovery for the recipient involves close monitoring, immune-suppressing medicines, and support through the weeks before counts recover. These patients are among the most vulnerable in hematological care, which is why each donation matters.
Key Takeaways
- A marrow harvest usually collects about one liter or less of marrow and blood.
- The amount is set by the recipient’s weight and capped by a limit based on the donor’s weight.
- What you give is a small share of your total marrow, and it regrows within weeks.
- Most donors now give by PBSC donation, which avoids anesthesia.
- Thorough screening protects donors, and serious complications are rare.
For more on the organ itself, see our bone marrow guide.
Frequently Asked Questions
Does donating bone marrow weaken your immune system?
No. Your remaining stem cells replace what was taken within a few weeks, and your immune system is not permanently affected. Blood counts may dip briefly after a marrow harvest, which is why donors are advised to rest and avoid heavy exertion for a short time.
Can you donate bone marrow more than once?
Yes, it is possible, although most registered donors never donate at all, and most who do give once. Registries set limits on repeat donations to protect donors. Our article on whether you can donate bone marrow more than once explains the rules.
How painful is bone marrow donation?
You are asleep or numb during a marrow harvest, so the procedure itself is not felt. Afterwards, most donors describe an aching lower back or hips, similar to a hard fall, that eases over days and responds to simple pain relief.
Who decides between marrow harvest and PBSC?
The recipient’s transplant doctor requests the source based on the patient’s disease and transplant plan. Donors are told which method is requested and can discuss any concerns with the collection center before agreeing.
