The tissue type is the combination of a group of proteins on the surface of your cells called human leukocyte markers (HLA markers). The immune system uses your HLA combination to identify each cell in the body as one of their own. Usually 8-10 markers are identified.
Once your HLA type is known, other people can have their blood tested to see whether their HLA type is the same as yours. The closeness of a match needed for a good result depends on which particular HLA markers are the same as yours. For some markers, doctors may accept small differences to improve the chances of finding an acceptable donor. This is known as a mismatched transplant.
Having a tissue type as close as possible to your own increases the chances of the transplant being successful. The closer the match, the less risk of your immune system rejecting the donor’s cells or the donor’s cells attacking your tissue.
Brothers and sisters (your siblings) are most likely to be a match for you, so if they’re willing to be donors they’re tested first. Each sibling has a 1 in 4 (25%) chance of having the same tissue type as you. When 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 perfect unless you have an identical twin. Parents, half-brothers and half-sisters will not usually be a good match.
Volunteer unrelated donor
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If you don’t have a match among your relatives, it may be possible to find a volunteer unrelated donor (VUD). Blood transfusion services and some charities have lists (registries) of volunteer unrelated donors in the UK. Our list of useful organisations can help you find them.
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, sometimes several months, and a suitable match is not always found.
Stem cells from cord blood
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After a birth, blood from the umbilical cord, which connects a baby to its mother during pregnancy, is a rich source of stem cells. Nowadays cord blood can be donated and stored so it’s available for people needing transplants.
It may be possible to use cord blood for people who don’t have a suitable HLA-matched sibling or VUD donor. With cord blood, you don’t need to have such a close match as with an adult donor, and it can be accessed quickly since it’s already frozen.
Your weight is an important issue when deciding if cord blood 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 for them from cord blood.
Likelihood of finding a match
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About 9 out of 10 (90%) white people from northern Europe find a match from a related or unrelated donor, or from cord blood.
People from black and minority ethnic groups often have difficulty finding a good match from volunteer registries because most people registered are white. Tissue types rarely match across different ethnic groups. Black and minority ethnic groups have about a 4 in 10 (40%) chance of finding a suitable match. This figure is lower if you’re mixed race.
Charities such as the Anthony Nolan Bone Marrow Trust and the African Caribbean Leukaemia Trust are working to recruit more donors from black and minority ethnic groups.