Finding a donor

Your donor is the person who gives their cells for your stem cell transplant. The first step in finding a donor is for you to have a blood test. This is to find out your tissue type. 

Your tissue type is made up of different proteins on the surface of your cells. These are called human leukocyte antigen (HLA) markers. Your immune system uses your HLA markers to recognise your own normal body cells.

Doctors use your HLA markers to match you with a donor. They compare your tissue type with close relatives, or with volunteer unrelated donors on a registry. Doctors look for the best matched donor available for you. 

Having the best possible match means less risk of:

The best match is usually a fully matched brother or sister (sibling).

Your donor does not need to have the same blood group as you. After the transplant, your blood group changes to their blood group.

If you don’t have a fully matched sibling, your doctors will look for alternative donors. This could be:

  • someone in your family
  • a relative whose tissue is a half match (haploidentical) to yours
  • someone on a donor registry.

Another option could be using a cord blood transplant.

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Stem cells from a matched related donor

Brothers or sisters each have a 1 in 4 (25%) chance of being a match. Our tissue types are a combination of both our parents’ genes. Not every combination is the same.

A different team from the one looking after you will contact your family to ask if they are willing to be tested. Your siblings can be tested even if they live abroad.

Stem cells from a volunteer donor

If you do not have a close match in your family your doctors will look for a volunteer donor who is not related to you. There are donor registries in the UK, such as Anthony Nolan, which have lists of possible volunteer unrelated donors.

If there is not a suitable UK donor for you, there are registries in other countries that your doctor can search. It usually takes longer to prepare a donor that does not live in UK. Occasionally no suitable donor can be found.

How to become a stem cell donor

You can find out more about how people become volunteer unrelated donors from these UK registries:

Half-matched donors (50% match)

Your specialist may advise using stem cells from a close relative whose tissue type is at least a 50% match to yours. This would happen if there is no matched donor (either family or unrelated) available. A close relative is a brother, sister, child, parent or half-sibling. Almost everyone will have at least one possible donor. This is called a haploidentical transplant.

As your donor is related, the transplant can usually be done quickly. But it is not suitable for everyone.

Because it is only a 50% match, there is more risk of complications in the first few months. These may include graft-versus-host-disease, slow recovery of the immune system and occasionally graft rejection. But doctors are finding different ways to manage these problems. For example, they can give chemotherapy again after the stem cell transplant. This helps to reduce the risk of GVHD by killing off the donor cells that can cause GVHD.

Stem cells from cord blood

Another source of stem cells is blood from an umbilical cord. This is the cord that connects a baby to its mother during pregnancy. Cord blood can be donated after birth and frozen. It is stored in a cord blood bank and used for people needing transplants. There is no risk to the mother or baby and all cord blood is tested to make sure it is safe to use.

It may be possible to use cord blood for people who do not have a suitable donor.

With cord blood, you do not need as close a match as with an adult donor. You can also get it quickly.

A person’s weight can be a factor when doctors are deciding whether a cord blood transplant is suitable. People who weigh more need more stem cells for a transplant to be successful. It may not always be possible to get enough stem cells from cord blood.

Sometimes doctors can use blood from two different cords in one transplant so enough stem cells can be given. This may be possible if both cords are a close match to each other, and a close match to you. This is called a double cord blood transplant.

Likelihood of finding a match

Most people who are white Europeans find a match.

But people from black, Asian and minority ethnic groups, without a related donor, often have difficulty finding a good match from volunteer registries. Most people registered as donors are white and tissue types rarely match across different ethnic groups. If you are mixed race, it can be more difficult.

Organisations and charities are working to increase the number of registered donors from all these groups (see "Stem cells from a volunteer donor" above). The numbers of volunteers have increased over the past few years. Cord blood banks have also increased the chances of finding a suitable donor.

How your donor will prepare

Donors are given counselling before they agree to donate stem cells. Once they understand what is involved, they are asked to sign a consent form. They can still change their mind after this.

Information about the donor is confidential and cannot be shared without their permission. This is the same for related donors and unrelated donors. They are looked after by a different team to you.

The donor has tests to make sure they are fit to donate and that it is safe for them. These include:

  • blood tests
  • a chest x-ray
  • checking their weight
  • an electrocardiogram (ECG) to check the heart.

They will also have blood tests to check:

  • their general health
  • for infections including HIV, hepatitis and cytomegalovirus (CMV).

Collecting the donor's stem cells

Your donor’s stem cells can be collected either from their blood or, less commonly, from their bone marrow.

Taking stem cells from the blood

The donor needs to have drugs to encourage their stem cells to move from the bone marrow into the blood. They have a small daily injection of a drug called a growth factor (G-CSF) under the skin. This is given for a few days leading up to the collection. It increases the number of stem cells in the bone marrow to make them move out into the blood. This is called mobilising the stem cells.

The nurses can show the donor how to give the injection themselves. Or they can have it at their GP practice or the hospital. The donor’s blood is checked after about 5 days of injections.

The collection

The stem cells are collected 1 or 2 days before the transplant. It takes 3 to 4 hours, usually as a day patient.

The nurse or doctor puts a cannula into a vein in each arm. The donor’s blood is removed through one arm and passed through a machine called a cell separator. This separates the stem cells and collects them. The remaining blood is then returned to the donor through the tube in their other arm. If there are not enough stem cells after one collection, the donor may have to come back the next day.

Taking stem cells from the bone marrow

Sometimes stem cells are taken from the donor’s bone marrow. This is usually from the back of the hip bones (pelvis). It is done under a general anaesthetic and usually means staying overnight in hospital.

Occasionally your donor may have their cells collected before you start your treatment. This may happen if your donor is away when your transplant is booked. In this case the cells are frozen until the day of transplant. They are defrosted when you need them.

About our information

  • References

    Below is a sample of the sources used in our stem cell and bone marrow transplants information. If you would like more information about the sources we use, please contact us at

    Carreras, Dunfour, Mohty and Kröger. The European Society for Blood and Bone Marrow Transplantation: Hematopoietic stem cell transplantation and cellular therapies. Springer, Switzerland. 2019. 

    FACT-JACIE International Standards for Hematopoietic Cellular Therapy – product collection, processing and administration. 7th edition. 2018. 

    Anthony Nolan. Operations and patient services user guide. Available from Accessed January 2019.

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Anne Parker, Consultant Haematologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

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