Matching Recipient and Donors
The use of the terms “match”, “matching” or a “perfect match” are often misunderstood or misused when referring to a recipient and donor.
A clearer way of describing the evaluation process between a recipient and donor would be to use the terms, “suitable” and “compatible”. A suitable donor is someone that is healthy enough to donate. A donor is compatible when, all the tests are finalized for the recipient and donor and it is shown that the prospective donor is able to donate to their recipient.
The history of the term “match” comes from the 6 HLA antigens, (Human Leukcyte Antigens.) In the past, 6 out of 6 antigens needed to match in order for the transplant to be successful. The new anti rejection drugs are so effective, that there isn’t a statistical difference in success rates between a zero match and a 5 out of 6 match. Therefore, HLA matching typically is not factor that determines whether someone is compatible. There is however, a benefit to having a “perfect match,” 6 out of 6 antigens since the life of the transplanted kidney survives significantly longer.
Donor and recipient matching is divided into three distinct areas: blood type matching, tissue type matching and cross matching.
Blood Type Matching
Scientists have known for many years that blood group matching is important in transfusion and it is equally important in kidney transplantation.
There are four major blood types in humans. These types are simply noted as blood type A, B, AB and O. Another factor, the Rh factor, adds a plus or a minus following the above blood type letter, so that everyone has a blood type such as A+ or B- and so on. The positive or negative feature in blood typing has nothing to do with the matching of a kidney between a donor and a recipient.
In most circumstances, a donor with blood type O is the universal blood donor. This means that a person with blood type O may donate to a person with any other blood type. Someone with blood type A may donate to a person with blood type A or AB and someone with blood type B may donate to a person with B or AB. A person with blood type AB may only donate to an individual who has that same blood type.
When you look at blood type matching from the kidney recipient's point of view, you get a different perspective. A recipient with blood type O can receive a kidney only from a donor with blood type O. A recipient with blood type A may receive a kidney from a recipient with blood type O or A and a recipient with blood type B can receive a kidney from a donor with blood type O or B, and a recipient with blood type AB can receive a kidney from a person of any blood type.
HLA/Tissue Matching (What the public commonly refers to as “Matching”)
Tissue matching has become quite complex and it relates essentially to genetic matching between donors and recipients. Proteins, called antigens, can be defined in blood tests and a set of antigens essentially creates a genetic profile of each individual.
Kidney transplant professionals currently define at least six specific antigens in each donor and recipient. These six antigens have been called the major histo-compatibility complex by some scientists. The compatibility aspect of that name relates to how a donor may be more or less compatible with any number of recipients.
Since there are six specific antigens, the best compatibility is a six-antigen match between a donor and a recipient.
The best long-term outcomes in kidney transplantation are directly related to matching. Therefore, the best long-term outcomes are between persons who share all six antigens, or those who are a six-antigen match.
Importantly, even in less perfectly matched organs respond and survive in the long term, when the kidney is from a living donor thanks to advanced in the effectiveness of the immunosuppressant drugs. This means that living donors who are not matched for any antigens (a zero match) may confidently donate knowing that the long-term outcomes for recipients of a zero-antigen matched organ, today, appear quite good. Similarly, poorly tissue-matched cadaveric organs may do quite well in many recipients. Obviously, individual characteristics must be taken into account when donor and recipient tissue matching are considered prior to a transplant.
Cross Matching
Cross matching is a very sensitive and final test performed on a kidney donor and a particular recipient. Laboratory techniques for cross matching have been refined and now enable scientists and physicians to define how a kidney transplant recipient may respond to particular cells or proteins of the kidney donor. These refinements in testing have led to very accurate tests that were not available even a few short years ago.
The basic cross match test involves a mixing of cells and serum to determine whether or not the recipient of a kidney will respond to the transplanted organ by attempting to reject it. In recent years, scientists have applied more intricate tests and obtained more accurate results of cross matching. It is now possible to better indentify a recipient who might reject an organ and thus avoid a transplant that might not succeed. Thus, improved kidney transplant outcomes may ensue because we can better determine and predict how the recipient may respond to the donated organ. Cross match testing, therefore, has evolved and improved long-term results.
Cross match testing, which involves several different phases and, as many as 10 to 15 different tests, comes down to a fairly simple final result. Either the cross match is positive or negative. A positive cross match means that the recipient has responded to the donor and that the transplant should not be carried out. A negative cross match means that the recipient has not responded to the donor and therefore transplantation should be safe. While this language may appear a bit backwards, we should all think of a cross match as the test indicating a “no go” or” go” for a transplant operation. A positive cross match (“no go’) essentially says the following to a recipient: you will respond to the donor organ by rejecting it and the operation should not be performed. A negative cross (“go”) match says to the recipient: you are not likely to reject the donor organ and the operation should be performed. If we look at the cross match in this way, the positive and negative results make sense to all concerned.
On balance, a well matched kidney is one in which the blood type between the donor and recipient are compatible, the tissue typing well defined and hopefully well matched and all cross match studies are negative. Application of good matching studies in clinical kidney transplantation has allowed for excellent results using living donor and cadaveric organs and has permitted safe kidney transplantation for thousands of patients with end-stage renal failure.
Plasmapheresis
More than one-third of willing live donors are turned down because their blood types are not compatible with the person to whom they wish to donate their kidney.
Most of us have natural antibodies against organs from people with different blood types. These antibodies can rapidly destroy a transplanted kidney.
Blood type incompatible transplant programs allow patients to receive a kidney from a live donor who has an incompatible blood type. Patients must be willing to undergo all prescribed treatments before and after the transplant to remove harmful antibodies and decrease the risk of rejection.
Blood Type Compatibility Chart
| Donor Blood Type | (can donate to) | Recipient Blood Type |
| O | - | A, B, AB, O |
| A | - | A or AB |
| B | - | B or AB |
| AB | - | AB |
Harmful antibodies are removed with a process called plasmapheresis, a procedure similar to dialysis that removes the plasma portion of the blood where antibodies are located. The number of plasmapheresis treatments required by the recipient before surgery varies depending on the amount of harmful antibodies in their blood.
After each plasmapheresis the recipient receives an intravenous infusion of immune globulin to replace antibodies needed to fight infections and help prevent harmful antibodies from returning. Once the antibodies against the donor’s blood type decrease to very low levels, the transplantation can take place.
To prevent the antibodies from returning and damaging the kidney, the recipient has several plasmapheresis treatments and doses of immune globulin after the transplant. In addition, the recipient’s spleen may be removed during the transplant procedure through tiny incisions. The spleen is the organ where antibodies are produced. A low level of antibodies may return after the transplant but does not appear to damage the new kidney.
After the transplant, the recipient is monitored for signs of rejection. This monitoring consists of regular clinic visits and twice weekly blood work to detect rising antibody levels, or decreasing kidney function. A kidney biopsy, in which small pieces of tissue are examined, also can detect rising antibody levels.
