What blood stem cell donors actually go through

Most people who join a blood stem cell registry never hear from it again. A small share get a call, sometimes years later, saying they may be the best match for a patient they will never meet. What follows is less dramatic than many people picture, and more involved than giving a pint of blood.

This walk-through follows the process used by NMDP, the US nonprofit that runs the country's national registry. Other registries work in broadly similar ways but set their own rules, so check details with the one you join. Nothing here is medical advice. The donor center's medical team decides who can safely donate.

Stage 1: Joining the registry

Joining NMDP takes a few minutes online and a cheek swab. You request a free kit, rub the swabs on the inside of your cheeks and mail them back in a prepaid envelope. A lab types your HLA genes, the immune markers used for matching, and your profile becomes searchable by transplant teams.

Age rules have changed over the years, so check them before you sign up. NMDP's join page currently says new members must be between 18 and 35. NMDP's stated reason is that cells from younger donors give patients a better chance of transplant success and long-term survival. Once you are on the registry, you stay listed until age 61 unless you ask to be removed.

You also answer health questions. Some conditions rule a person out, either to protect the donor or to protect the patient. If you are unsure about something in your history, it is far better to ask before joining than to find out when a patient is waiting.

Think about commitment at this stage too. You can withdraw at any point, but timing matters. Before a transplant, the patient receives chemotherapy or radiation that wipes out their own blood-forming system. A donor who pulls out after that has started leaves the patient in grave danger. Saying no early, at the swab stage or on the first call, costs the patient far less.

Stage 2: The call

If a patient's search turns up your profile, the registry contacts you. That might happen within months, after many years, or never. Keep your phone number, email and address current. To a patient, an unreachable donor is the same as no donor.

The first conversation checks that you are still willing, runs through some health questions and asks about your availability over the coming weeks. You will learn only a few facts about the patient, typically their age, sex and diagnosis.

Stage 3: Confirmatory typing

Next comes a blood sample, usually drawn close to home. This step is called confirmatory typing. The lab repeats your HLA typing in more detail to confirm the match and tests for infectious diseases. Several potential donors may be tested for the same patient, and the transplant team picks one. Being asked for a sample does not mean you will be chosen.

Matching involves more than HLA. Transplant teams also weigh donor age, sex, blood type and factors such as cytomegalovirus (CMV) status. Some patients have a much harder time finding any close match, for reasons explained in our piece on cord blood, genetic diversity and finding a match.

Stage 4: Information session and health screening

If you are selected, a donor center staff member walks you through what lies ahead in an information session, and you can bring a partner or family member. You then sign a consent form and have a physical exam and blood tests. The exam checks that donation is safe for you and that nothing you carry could harm the patient.

The patient's doctor requests one of two donation methods, based on what suits the patient's disease and treatment plan. According to NMDP, about 90 percent of its donors give peripheral blood stem cells (PBSC), and about 10 percent are asked for bone marrow.

NMDP estimates the whole process takes an average of 20 to 30 hours of your time, spread over 4 to 6 weeks, not counting travel.

Stage 5: Donation day, two ways

Peripheral blood stem cells (PBSC)

Blood-forming stem cells normally live in the bone marrow, with only a few circulating in the blood. To push more of them into the bloodstream, PBSC donors receive daily injections of filgrastim, or an FDA-approved similar medicine, for the 5 days leading up to collection. Filgrastim is a growth factor that stimulates the marrow. The injections are usually given by a nurse at a clinic, though arrangements vary.

Collection uses apheresis, the same kind of machine used for platelet donation. Blood leaves through an IV in one arm, passes through a machine that separates out the stem cells, and returns through an IV in the other arm. NMDP says most PBSC donations take 4 to 8 hours and are finished in one session; some donors need a second day. Occasionally, when arm veins are not suitable, a temporary catheter is placed in a larger vein instead.

NMDP's page on donating PBSC describes each step in more detail.

Bone marrow

Marrow donation is a surgical procedure in a hospital operating room. Nearly all donors receive general anesthesia, and some receive regional anesthesia instead. Doctors use needles to withdraw liquid marrow from the back of both sides of the pelvic bone. The procedure usually takes 1 to 2 hours. Most donors go home the same day, though some hospitals plan an overnight stay.

Your body replaces the donated marrow on its own within a few weeks. NMDP's page on donating bone marrow has the full description.

Side effects and recovery

Here is how the two methods compare, using figures NMDP publishes for its donors:

Two points from NMDP's figures stand out. Serious complications are rare, under 1 percent of donors for either method. And back or hip pain after marrow donation is very common, reported by more than 80 percent of marrow donors, so plan for a few sore days and some help at home. NMDP gives the median time to full recovery after marrow donation as about 20 days.

The donor center checks in with you after donation until you have recovered, and registries keep collecting data on donor health over the longer term.

Costs

Donors do not pay to donate. NMDP says it covers all travel and donation-related costs, including flights, hotels and meals, and that this can extend to childcare, pet boarding, lost wages and travel for a friend or family member who comes with you. NMDP does not pay donors for the cells themselves.

Some US states give employees leave for marrow or stem cell donation, and some employers have their own policies. Ask your human resources team early, because the scheduling window can be short.

Anonymity and contact later

US unrelated donations are confidential. As a donor you learn a few basics about the patient, and the patient learns limited, non-identifying information about you. Where the patient's transplant center allows it, you may receive brief updates during the first year, such as whether the cells engrafted.

For the first 12 months, you and the patient can exchange anonymous cards, letters or emails through your donor center. Names, nicknames, initials, hospitals, employers, locations, photos and personal dates are not allowed. After a year, if both of you sign consent forms, you can be put in touch directly. Rules differ abroad: some countries and transplant centers never allow direct contact, and some share no updates at all. NMDP's page on contacting your recipient sets out the current rules.

Frequently asked questions

Does it hurt?

Joining does not. PBSC donors often feel achy during the injection days, much like a mild flu, and may notice tingling around the mouth or fingers during collection, which staff watch for and can usually ease. Marrow donors are under anesthesia for the procedure itself and are usually sore in the lower back or hips for some days afterward.

Can I choose which way I donate?

The request comes from the patient's doctor, who picks the method that best suits the patient. You can talk through concerns with your donor center, and you remain free to decline, but you cannot simply swap one method for the other.

Could I be asked to donate again?

Sometimes. A patient may later need a second stem cell donation, or a donation of white blood cells (lymphocytes), from the same donor. You can say yes or no at that point too.

What happens to my cells after collection?

A courier usually carries them to the patient's transplant center, where they are infused fresh or frozen for later use. How collected cells are counted, processed and frozen is covered in our page on stem cell technology.

What diseases are these transplants used for?

Blood stem cell transplants are used for some leukemias and lymphomas, marrow failure such as severe aplastic anemia, and a range of inherited blood and immune disorders. Our guide to conditions treated with cord blood transplants explains what the long disease lists you see online actually mean, and the same logic applies to adult donor transplants.

I am over 35. Is there still a way to help?

Not by joining NMDP's registry under its current rules, though other registries set their own age limits. Relatives of a patient can be tested as related donors through the patient's transplant center at other ages. Blood and platelet donation help transplant patients directly, since many need transfusions during treatment.

I joined years ago. Is there anything I should do now?

Yes, three small things. Log in or call to update your phone number, email and address. Tell the registry about any major health change, so a match is not delayed by a surprise at screening. And decide now whether you would still say yes, because a quick, clear answer on the first call gives the patient's team the most time.