What Is a Stem Cell Donor Registry, and How Does Matching Work?

For most people, "stem cell donor" calls to mind a cheek swab and a vague sense they might someday get a call. This article explains what a stem cell (bone marrow) donor registry is, how organizations such as NMDP (formerly Be The Match), the World Marrow Donor Association (WMDA), and DKMS use HLA typing to match donors to patients, what joining involves, how likely a registrant is to ever be called, and how public umbilical cord blood banking fits in as a related stem cell source.

What a Donor Registry Actually Is

A stem cell or bone marrow donor registry is a searchable database of volunteers whose tissue type has been recorded, who have agreed to be contacted if their cells could help a patient they will likely never meet. Registries don't treat patients; they connect a transplant doctor with a matching, willing, healthy donor anywhere in the world. Major registries include:

• NMDP (National Marrow Donor Program), operating as Be The Match in the U.S., founded 1987. It runs the federally supported registry under the C.W. Bill Young Cell Transplantation Program, reporting over 22 million registered donors plus hundreds of thousands of banked cord blood units.
• DKMS, a German-founded nonprofit now among the world's largest donor-recruitment organizations, with affiliates in the U.S., UK, and elsewhere.
• WMDA (World Marrow Donor Association), founded 1986, sets international standards and runs a "Search & Match" service letting member registries search each other's pools. Its network links roughly 75 registries across 50+ countries, together listing more than 38 million potential donors.
• National registries elsewhere (Anthony Nolan in the UK, Canadian Blood Services, etc.) that maintain their own pools and cooperate through WMDA.

Because any one country's registry may lack a match for a given patient, these organizations share data internationally, so a patient often receives cells from a donor registered on the other side of the world.

HLA Typing: The Science Behind a "Match"

Matching isn't based on blood type but on Human Leukocyte Antigen (HLA) markers — proteins on cell surfaces that let the immune system distinguish "self" from "foreign." Each person inherits one set of HLA markers from each parent, and physicians typically compare donor and patient at 7 to 10 specific markers (an "8/8" or "10/10" match) via a DNA-based test. A closer match lowers the risk of graft-versus-host disease and rejection. Because HLA is inherited, siblings have roughly a 1-in-4 chance of fully matching each other, and about 70% of patients needing a transplant have no matched relative — why volunteer registries exist.

HLA types also cluster by ancestry, which is why registries recruit across racial and ethnic groups. A widely cited 2014 New England Journal of Medicine analysis (Gragert et al.) estimated the likelihood of finding a well-matched (8/8) adult donor at roughly 75% for patients of white European ancestry, versus roughly 16–19% for Black patients of Caribbean or African ancestry, with other groups in between. These figures are over a decade old and likely improved as registries diversified, but the pattern — longer odds for underrepresented ancestries — still drives recruitment.

How to Join a Registry

Joining is intentionally simple. You register online or at an in-person drive, swab the inside of your cheeks with a mailed kit, and mail it back — no blood draw needed at this stage. A lab extracts DNA from the swab, performs HLA typing, and enters the results into the registry (your identity stays confidential from patients). Eligibility windows vary: most registries accept joiners roughly age 18 to 40–44, with some allowing up to around 60, plus basic health screening. You stay listed until an upper age cutoff — NMDP keeps registrants until 61 — or until you withdraw, generally possible at any time.

What Happens If You're Identified as a Match

A preliminary computer hit doesn't guarantee you'll donate. Roughly: a coordinator contacts you to confirm interest; you give a more thorough confirmatory HLA test; if you remain a strong candidate, you attend an information session (often around 90 minutes) and a full health screening. If cleared, you donate by one of two methods, depending on what the patient's doctor requests:

• PBSC donation: non-surgical. Daily filgrastim injections for about five days push stem cells into the bloodstream, then apheresis filters them out via a machine over several hours, usually in one session.
• Bone marrow donation: a surgical procedure under anesthesia, withdrawing liquid marrow from the pelvic bone. Most donors go home same-day and resume normal activity in one to seven days, though soreness can linger.

You can change your mind at any point, but registries note that patients undergo intensive, sometimes dangerous pre-transplant conditioning, so a late withdrawal can seriously harm the patient — hence the emphasis on committing before joining.

How Likely Are You to Actually Be Called?

Most registrants are never called. Registries are candid that individual odds are low, since a match requires a rare combination of markers to align with a specific patient's needs at the right time. DKMS's UK affiliate states registrants have roughly a 1-in-800 chance of ever being matched and donating, noting real odds vary with age, sex, and HLA type. Younger male donors are disproportionately requested because their cells are linked to better outcomes; U.S. registries report doctors request donors aged 18–44 more than 90% of the time. In short, a typical donor waits years, if called at all — though registrants with less common HLA profiles may hear back sooner.

Umbilical Cord Blood Banking: A Related Source

Umbilical cord blood — left in the placenta and cord after birth — is also rich in blood-forming stem cells and can substitute for bone marrow or PBSC cells in some transplants. It's collected painlessly from tissue that would otherwise be discarded. There are two paths:

• Public banking: parents donate at no cost; the unit is HLA-typed, listed on a registry such as NMDP's, and available to any matching patient worldwide (or used for research if it doesn't meet transplant standards).
• Private banking: parents pay collection and storage fees so the unit is reserved solely for their own family and cannot be added to a public registry.

Cord blood tolerates a somewhat less precise HLA match and is immediately available once identified, but each unit holds a limited cell supply, making it less suited to larger patients. Public cord blood banks function as part of the same global matching system as adult donor registries, drawing on a different source.

Bottom Line

A stem cell donor registry is essentially a matchmaking database: it stores HLA types for millions of volunteers and banked cord blood units so physicians can search for the closest genetic match for a patient, usually a stranger. Joining takes only a cheek swab, but actual donation happens only for the relative few whose tissue type lines up with a specific patient — a low-probability, often years-long wait for most, if it happens at all. Because HLA types cluster by ancestry, registries keep prioritizing a broad, diverse donor pool so patients of every background have a realistic shot at a match. Anyone considering registering, or donating cord blood after a birth, should get current eligibility details directly from an established nonprofit registry such as NMDP/Be The Match, DKMS, or their national equivalent.