How is blood matched for bone marrow transplant?

You have a blood test to match blood before a bone marrow transplant. This page tells you why matching blood is important. 

Bone marrow or stem cell transplants are most often used to treat leukaemia and lymphoma. But they can be used for some other types of cancer.

In a bone marrow or stem cell transplant you have high doses of chemotherapy and sometimes radiotherapy. The treatment destroys the stem cells that make blood cells in the bone marrow. So after the transplant you need to have stem cells given back to you by drip into the bloodstream. The stem cells make their way into the bone marrow and start making blood cells again. There is detailed information about bone marrow transplants and stem cell transplants in our cancer treatment section. 

Some people have their own stem cells back after a transplant. But some people have stem cells or bone marrow from a donor. If you are going to have stem cells from a donor your doctors need to make sure that your donor's blood cells are as similar to yours as possible. If the stem cells are very different your immune system will try to destroy the donor cells and they then won't be able to make blood cells. 

So before you have a transplant, you and your donor have blood tests. Laboratory staff check the surface of your blood cells and the donor blood cells for certain proteins. The proteins are called HLA markers or histocompatibility antigens. So the test is called HLA typing or tissue typing. Everyone has their own set of proteins. Staff compare the proteins on the cells in the blood samples to see how many of the HLA markers are the same. Members of your close family are the most likely to have similar proteins to yours. Usually 6 or 8 HLA markers are checked before a bone marrow or stem cell transplant. 

The results of your blood test and the donor's test tell your doctor how good the HLA match is between you. You can have a transplant without a perfect match. This is known as a mismatch. If you have a mismatched transplant, you will be more likely to have a reaction after the transplant called graft versus host disease (GVHD). This means the immune cells from the donated marrow or stem cells attack some of your body cells. GVHD typically causes skin rashes, diarrhoea and liver damage. It is usually quite mild and you will be given anti rejection drugs to help stop it developing. But GVHD can be severe and even life threatening in some people.

GVHD is not always a completely bad thing. As it is an immune system reaction, mild GVHD can help to kill off any cancer cells that are left after your treatment.