Board approves changes to immunologic matching

Published on: Thursday, December 14, 2006

Tucson, Ariz., December 14, 2006 --The OPTN/UNOS Board of Directors approved a policy modification expected to improve the efficiency of organ allocation by better identifying and prioritizing candidates whose immune system would likely reject an organ offer. The OPTN will now utilize a statistically calculated formula to identify immunologically "sensitized" candidates rather than relying solely on individual laboratory testing of candidate blood samples.

"This new approach will provide a much more accurate estimate of the numbers of potential donors with whom a transplant candidate may be compatible," said M. Sue Leffell, Ph.D., chair of the OPTN/UNOS Histocompatibility Committee.

Immune sensitivity is most crucial to kidney and pancreas transplantation but can affect other organ transplants as well. Certain transplant candidates are considered "sensitized" because their immune systems react to a wide number of human leukocyte antigens (HLA) present in potential donor organs. As a result, they would be likely to reject many potential organ offers.

Traditionally, immune sensitization has been measured by a panel reactive antibody (PRA) test performed by a laboratory to determine the percentage of organ donors to which a transplant candidate has specific HLA antibodies. Kidney transplant candidates who are highly sensitized (a PRA of 80 percent or higher) are given additional allocation priority points to increase their opportunity of an allocation match that would not lead to short-term organ rejection. Laboratory tests vary in how PRA is reported based on differences in their techniques and in the timing of blood samples recovered from transplant candidates.

Under the newly approved policy, PRA will be calculated according to a scientifically based formula that uses the frequency of specific, known unacceptable HLA antigens reported for a transplant candidate to determine his or her overall immune sensitivity. Sensitized transplant candidates must have unacceptable antigens specified to receive additional allocation priority. This process is expected to create greater consistency in identifying PRA among transplant candidates and assure greater accuracy in prioritizing those with high levels of sensitization.

In related action, the OPTN/UNOS Board approved the incorporation of calculated PRA into the pancreas allocation policy. Pancreas transplant candidates with a calculated PRA of 80 percent or greater will be given allocation priority over less sensitized candidates at each level of organ allocation (local, regional and national).

Among other deliberations, the Board discussed work in progress to strengthen and streamline oversight of OPTN/UNOS members' policy compliance and patient safety, as well as a significant revision of the nation's kidney allocation system. Specific proposals on these topics will be developed and circulated for public input in early 2007.

The Organ Procurement and Transplantation Network (OPTN) is operated under contract with the U.S. Department of Health and Human Services, Health Resources and Services Administration, Division of Transplantation by the United Network for Organ Sharing (UNOS). The OPTN brings together medical professionals, transplant recipients and donor families to develop organ transplantation policy.