The first step in finding a donor is taking a blood test from you to identify your tissue type. Your tissue type is the combination of proteins on the surface of your cells called human leukocyte antigen (HLA) markers. Your immune system uses your HLA markers to recognise cells in the body as your own.
Blood tests usually identify 8–10 markers. Once your tissue type is known, other people can have their blood tested to see whether their tissue type is the same as yours. Having a close match to your tissue type increases the chances of the transplant being successful. The closer the match, the less risk of the donor’s cells attacking your cells, or of graft failure.
You don’t have to be the same blood group as your donor.
After the transplant, your blood will change to their blood group.
Brothers and sisters (your siblings) are most likely to be a match for you. They will be contacted to ask if they are willing to be tested. This will be done by a different medical team from the one looking after you. Your siblings can be tested even if they live abroad. Their blood sample can be taken by their doctor or local hospital.
Each sibling has a 1 in 4 (25%) chance of having the same tissue type as you. If one of your siblings is completely matched to you, they are known as an HLA identical donor. But the match is unlikely to be exactly the same unless you are identical twins.
For some markers, doctors may accept small differences to improve the chances of finding a donor. This is known as a mismatched transplant.
Parents, half-brothers and half-sisters will not usually be a good match.
Volunteer unrelated donor
If you don’t have a match among your relatives, your doctors can look for a volunteer unrelated donor (VUD). There are donor registries in the UK which have lists of possible volunteer unrelated donors.
There are a large number of registries in other countries that your doctor can also search if there’s no suitable UK donor for you.
But this can take time and a suitable match is not always found.
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 and stored in a cord blood bank, so it’s available for people needing transplants. There is no risk to the mother or baby.
All cord blood is tested to make sure it is safe to use. It may be possible to use cord blood for people who don’t have a suitable donor. With cord blood, you don’t need to have as close a match as with an adult donor. And because it is already stored it can be accessed quickly.
Your weight is important when deciding whether a cord blood transplant is suitable. People who are heavier need more stem cells for a successful transplant, and it’s not always possible to get enough stem cells from cord blood.
Sometimes doctors can use cord blood from two different cords in one transplant if they are both a close match. This is called a double cord blood transplant.