Matching Kidney Donor to Recipient
The degree to which the tissue of the donor matches that of the recipient is a critical factor in the life expectancy of the transplanted organ. This matching is comprised of two systems: the blood and the tissues. The rules for blood-type are the same as for blood transfusions:
- Recipients with type A blood can receive from donors with types A and O.
- Recipients with type B blood can receive from donors with types B and O.
- Recipients with type AB blood can receive from donors with types A, B, AB and O.
- Recipients with type O blood can receive from donors with type O only.
The Rhesus factor (positive or negative) is not relevant in kidney donation.
A technique which allows transplants even from non-matching donors has been developed in recent years. This technique, which requires that the patient undergo a series of preliminary treatments, is available only at selected medical centers.
In the case of tissue matching, the chances of success and survival increase with the quality of the match. Perfectly matched tissue exists only between identical twins which makes them the best candidates for transplants.
Development of anti-rejection drugs has improved the chances of success where the tissues are not completely matched. The percentage of successful transplants from living donors is relatively high, even in cases where the tissues are only partially matched.
When the donor is not alive, the chances of success are smaller and tissue-matching is more critical.
The Immune System’s Reaction to Kidney Transplantation
Antibodies are essentially proteins produced by the immune system to protect the body from any foreign “invasion” such as the transplanted kidney. The most severe reaction is liable to occur when the patient has already received tissue from other outside sources such as non-matching blood transfusions or previous transplants. The antibodies cannot distinguish between dangerous bacteria or viruses and the tissue of an organ which is vital to the body’s function. The more the body has been exposed to foreign tissue, such as after pregnancy or blood transfusion, the wider variety of antibodies it produces, making it harder to find a matching donor.
It sometimes happens that at the point during the transplant when the surgeon attaches the patient’s blood circulation to the renal artery the antibodies cause blood clots in the tiny arterioles of the donated kidney. Such cases are life-threatening and the kidney must be immediately detached. This situation is prevented in advance by cross-checking if the patient’s blood contains antibodies against the tissue of the transplanted kidney. If there is a positive cross-match, the surgery cannot take place.
To reduce the possibility of rejection due to antibodies, the patient must undergo a number of treatments to suppress his immune system. These might include plasmapheresis, intravenous immunoglobulin and sometimes even radiation therapy or medications to neutralize the antibodies in the blood (cortisone, etc.). After surgery the patient’s immune system must be rehabilitated. Otherwise any virus could be life-threatening. He must be kept in a hygienic environment that has been thoroughly disinfected.
It is important to understand that any transplanted organ is eventually rejected by the body because the tissue cells of the donor are not identical to its own. It is only a question of time until the body develops antibodies and becomes immune. At some point the body develops a chronic rejection mechanism, but until that happens, the patient can benefit from his improved health.