Research shows the ideal source of kidney transplants is a live donor. Live donation can be scheduled at a time most convenient for the donor and recipient and when both parties are in optimal health. Recipients of living donor kidneys tend to have longer organ survival rates and a better quality of life.

Sometimes a transplant candidate doesn't have someone who can, or is willing, to donate a kidney. The patients are then placed on the national transplant waiting registry but there aren't enough deceased donors to meet the needs of those waiting for a new organ. As of June 8, 2007, there were 72,088 people on the waiting list for a new kidney. Researchers estimate, in a given year, only 25 percent of those waiting for a kidney get a transplant. About six percent of patients on the kidney waiting list die before a donor organ becomes available.

Making a Match

When a donor organ becomes available, it must be matched with a recipient to decrease the risk of rejection or complications. The first match criteria is based on blood type. The second is for HLA (human leukocyte antigen), a type of genetic marker on white blood cells. We have six sets of HLA factors, three inherited from each parent. The higher the number of HLA matches, the greater the likelihood of a successful transplant.

Another important consideration in transplant matching is the presence of HLA antibodies in the recipient (called HLA sensitization). Antibodies are produced by the immune system in response to an earlier encounter with foreign tissue, like a virus or bacteria. Antibodies can also form when a person is exposed to foreign tissues, as with a pregnancy, blood transfusion or previous transplant. Thus, a person with an HLA antibody is likely to react against a donor organ having that HLA antigen.

Researchers estimate about 30 percent of people on the transplant waiting list have some HLA sensitization. The higher the degree of sensitization, the harder it is to find a compatible donor organ. About 7000 people on the kidney waiting list have a high number of HLA antigens. These "highly sensitized" candidates are at risk of having an immediate rejection of a donor kidney.

Increasing the Chance of a Match

Traditionally, when a donor kidney becomes available, it is allocated through a point system that takes into consideration a candidate's waiting time, HLA matching and sensitization. So highly sensitized patients, who may have antibodies against many of the potential donor organs, often face a very long wait.

Researchers at Emory University hope to improve the kidney allocation system by helping highly sensitized patients find an appropriate match. The investigators have developed an algorithm to help doctors predict which sensitized candidates will most likely be compatible with a donor. They use a new type of technology that enables doctors to identify individual HLA antibodies, instead of the traditional broad screen that identifies groups of antibodies. The information can be used to more precisely cross-match a candidate with a potential donor. In a study published last October, the researchers found the algorithm was very successful in predicting the outcome of a transplant in highly sensitized patients. Graft survival rates were similar (66 to 70 percent) among unsensitized, moderately sensitized and highly sensitized recipients.

Pathologist, Robert Bray, Ph.D., says the algorithm doesn't guarantee there will always be a match for a highly sensitized patient. But the formula improves the odds of a match by assuring doctors a transplant is likely to be successful. Thus patients may not be passed over for selection when a kidney becomes available. The algorithm may also widen the pool for candidates. Currently, a transplant center may be reluctant to send a donor organ over a great distance for fear of the chance of rejection and "wasting" the organ. But if doctors can say with greater certainty that an organ will be compatible, the organ may go to the highly sensitized patient at the top of the list rather than the next person on the waiting list.

For information on kidney disease or kidney transplantation:

National Kidney and Urologic Diseases Information Clearinghouse

National Kidney Foundation

For general information on organ transplantation:

United Network for Organ Sharing