For a kidney transplant to be successful, it is essential that the tissues of the new kidney are fairly similar to the patient's original kidney. This helps stop the body's natural defense system from rejecting the transplant.
Before a suitable kidney can be found, it is necessary for patients to have a number of tests. The results will then be checked against the results of similar tests carried out on an available kidney, or on a person considering donating a kidney to the patient.
Tests prior to transplantation
- Matching blood group
A simple blood test establishes which one of the four main blood groups—A, B, AB, or O—a patient or a donor belongs. Your immune system will attack a kidney from a blood group that is not compatible with your own. You can only be given a transplant kidney if your blood group matches that of the donor, as follows:
This table shows compatible blood groups
Patient Donor Group A Group A or O Group B Group B or O Group AB Group A, B, AB or O Group O Group O Note that blood group O is a match for all of the other groups.
- Matching tissue type
Matching donors to recipient by type of tissue is desirable. The better the match, the greater the chances of the kidney transplant lasting a long time. A perfect match, however, is not essential.
Tissue type is usually determined by looking at 6 different proteins in the body. Different people have different versions of these proteins. Tissue type is established using a blood test. Since the number of possible tissue types is much more numerous than for blood groups, the chances of finding a perfect match is less than with matching blood groups.
It is extremely rare to be able to get an exact match of tissue type between donor and patient. Doctors will usually consider doing a transplant if at least half of the donor's tissue-type proteins match the recipient's.
- Testing for viruses
A candidate for a transplant goes through a series of blood tests to check for various viruses, such as HIV, hepatitis B, hepatitis C, and cytomegalovirus. These viruses may be present and inactive in the patient's body, but the transplant and immunosuppressant drugs could activate them, causing illness.
HIV testing will not be carried out without the patient's consent. A patient, who refuses any of the tests including HIV, may not be allowed to have a transplant. If one of these viruses is found, doctors may still allow the patient to have a transplant, but will monitor the patient particularly carefully.
Other tests that may be necessary before a patient can be put on the waiting list for a transplant include:
- an electrocardiogram (ECG), an electric recording of the heart
- an echocardiogram (echo), a sound-wave picture of the heart
- a chest X-ray
Patients with diabetes are sometimes required to have a cardiac catheter test (special X-ray picture of the heart).
When a suitable kidney is found, two further tests will be required before the operation:
- Physical examination. The physical exam will determine the general health of the patient. It may be too risky for a patient with a bad cold to have the anesthetic. Such a patient will be sent home and put back on the waiting list.
- Cross-match. This is the final test to be passed before a transplantation operation can go ahead. A cross-match is a blood test to check that the patient does not have antibodies that will react with the donor kidney. The test is done by mixing a sample of the patient's blood with cells from the donor's lymph nodes or spleen. If there is no reaction, the operation proceeds. If there is a reaction, which is known as a positive cross-match, the transplantation cannot go ahead.
Tests after transplantation
After a transplant regular tests will be performed to make sure that the kidney is working well (these are the same as the blood and urine tests described in the pre-dialysis section) and that you are having the correct amount of drugs to prevent the kidney from rejecting. The levels of these drugs can be tested by a simple blood sample.
May 1, 2006