What blood tests will I need to find out if a patient and a potential donor are a kidney match.
There are three main blood tests that will determine if a patient and a potential donor are a kidney match. They are blood typing, tissue typing and cross-matching.
What is Blood typing (ABO compatibility)?
Blood typing is the first blood test that will determine if your blood is compatible with the potential donor's blood.
If the donor's blood type works with your blood type, the donor will take the next blood test (tissue typing). If blood types are not compatible, the donor will not be able to donate directly to you. However, the donor may consider donating through a paired exchange program which would allow you to get a kidney from another donor who is not a match for their intended recipient. Talk with your transplant coordinator for more information and additional support.
Kidney donors must have a compatible blood type with the recipient. The Rh factor (+ or -) of blood does not matter in a transplant.
The following blood types are compatible:
- Donors with blood type A… can donate to recipients with blood types A and AB
- Donors with blood type B… can donate to recipients with blood types B and AB
- Donors with blood type AB… can donate to recipients with blood type AB only
- Donors with blood type O… can donate to recipients with blood types A, B, AB and O (O is the universal donor: donors with O blood are compatible with any other blood type)
- Recipients with blood type O… can receive a kidney from blood type O only
- Recipients with blood type A… can receive a kidney from blood types A and O
- Recipients with blood type B… can receive a kidney from blood types B and O
- Recipients with blood type AB… can receive a kidney from blood types A, B, AB and O (AB is the universal recipient: recipients with AB blood are compatible with any other blood type)
What is Tissue Typing?
This blood test is done in a laboratory monthly while waiting for a transplant and also immediately before a transplant surgery to see if the tissues of the donor are compatible with those of the patient. Each person's tissues, except for identical twins, are different from everyone else's. It is believed that the better the tissue match, the more successful the transplant will be over a longer period of time.
Children inherit a set of 21 chromosomes from each parent. These chromosomes are the structures within your cells that contain the genetic material that determines who you are. The sixth chromosome carries the antigens that are important in kidney transplants. An antigen is a genetic marker. Genetic markers are unique to your body. You may hear these called HLA, or human leukocyte antigens. The process of identifying these antigens is called tissue typing. The leukocytes, or white cells, in your blood carry these antigens and are used to identify them. More than 7,000 to 8,000 combinations of known antigens are possible.
Because you inherited a sixth chromosome from each parent, either parent could donate a kidney to you as long as he or she is healthy and has a blood type that is compatible with yours. A brother or sister could also be compatible if he or she inherited the same combinations as you did. A parent and child would have at least 50 percent match while siblings could have a zero to 100 percent match. The best match for the recipient is to have six out of six antigens match. (This is known as a zero mismatch.) It is possible for all six markers to match.
What is Percent Reactive Antibody (PRA)?
This is another term you will hear often while being evaluated for a transplant. When you are exposed to antigens, either through a blood transfusion, pregnancy or previous transplant, you may develop an antibody to these antigens. It is important to test for the presence of these antibodies before your transplant. If you have a high level of antibodies, it may be more difficult to find a compatible kidney for you. However, new procedures such as plasmapheresis may be able to reduce the antibodies in your blood.
What is a Serum Crossmatch?
A serum crossmatch is a blood test you and the donor will have multiple times, including right before the transplant surgery. This test takes about four to five hours to complete. To do the test, cells from the donor are incubated with your serum. If your serum has antibodies against the donor's cells, the cells will be destroyed. This is called a positive crossmatch and it means that the transplant cannot take place. To do so would result in immediate rejection of the transplanted kidney.
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© 2014 National Kidney Foundation. All rights reserved. This material does not constitute medical advice. It is intended for informational purposes only. Please consult a physician for specific treatment recommendations.