Allocating Deceased Donor Kidneys to Sensitized Candidates.

In this edition of the Clinical Journal of the American Society of Nephrology, Gebel et al. (1) present simulation data showing that the new kidney allocation system (KAS) increases the offer rate for highly sensitizedkidney transplant candidates. This is counter to the previously held belief that the only possibility of transplanting a highly sensitized patient iswith anHLA-identical kidney. The modeling by Gebel et al. (1) shows that even a candidate with calculated panel–reactive antibody (cPRA) of 100% has multiple potential donors. This is consistent with European data and the early results of the KAS that went into effect on December 4, 2014 (2,3). This observation is notable, and it is valuable for the general nephrologist to understand both how and why this new approach to the highly sensitized patient was developed as well as the consequences that stem from it. Among the many changes to kidney allocation are a new sliding–scale point system and larger geographic sharing of kidneys for highly sensitized candidates. Such patients are those who formed anti-HLA antibodies through events, such as prior solid organ transplantation, blood transfusion, or prior pregnancy, and are unable to receive transplants from some or most organ donors because of immunologic incompatibility. There are many myths about these highly sensitized patients. It is often assumed that all of these patients have already received a kidney transplant and are now seeking a second, third, etc. However, the reality is that nearly 40% of them are being waitlisted for their first transplant and require additional priority in allocation to receive a transplant (D. Stewart, personal communication). The intent of this change was to provide improved access to transplantation for these patients. To develop a sliding–scale point system for degree of sensitization, the Organ Transplantation Network (OPTN) /United Network for Organ Sharing (UNOS) Kidney TransplantationCommittee studied the time to next offer (how long a patient would be expected to wait for a second offer if the first offerwas declined) for sensitized patients. The intent was to determine the value for cPRA at which a recipient becomes truly become disadvantaged. The time to next offer analysis results were unexpected and dramatic. The median time for a patient with cPRA at 0% is 11.7 days. The effect of sensitization level escalates as cPRA increases into the 60%–69% decile, with the median time more than doubling to 31.2 days. It nearly doubles again to 55.2 days when cPRA reaches 75%–79%. As the cPRA increases to.90%, there are large increases in the time to next offer. An increase from 95% to 97% results in a near doubling of the estimated median time from 175 to 330 days, and increasing cPRA by an additional two points to 99% triples the time to 993 days.Most striking is the observation that, for a patient with cPRA of 100%, the median time to next offer increases to 4969 days or .13 years. The allocation system in existence before December 4, 2014 allocated a lump sum of four allocation points to individuals with a cPRA of.80%. Therefore, in this system, a patient with cPRA of 80% and onewith cPRA of 100% are treated exactly the same. The additional four points resulted in individuals with cPRA between 80% and 95% receiving an increased access to transplantation, whereas for those candidates with cPRA of .95%, these four additional allocation points did nothing to change the rate of transplantation (4). To correct this imbalance in access to kidney transplantation caused by sensitization, the KAS uses both a sliding–scale point system and a tiered systemof larger geographic sharing. The sliding–scale point system exponentially assigns additional allocation points beginning at a cPRA of 20%, when a candidate receives an additional 0.08 points up to a maximum of 202.10 points for a candidate with cPRA of 100%. The tiered geographic sharing allows candidates with cPRA of 100% access to all kidneys recovered nationally; those with cPRA of 99% have access to kidneys recovered regionally, and for individuals with cPRA of 98%, the additional 24.4 points that they are allotted place them first on the local (donor service area) list (5). The intention of this combined approach is to ensure from the time of listing that these candidates are placed at the top of their respective allocation pools so that they will immediately start receiving offers. The results of this approach are consistent with the modeling done by Gebel et al. (1). In the first few months of the KAS, the transplant rate for patients with 98%–100% cPRA increased dramatically,whereas the transplant rates for candidates with cPRAs of 80%– 96% fell back to be proportional with their representation on the waiting list, thus both improving access for those truly in need and undoing the unintended advantage given to others. This bolus effect was predicted, and in themonths since theKASwas initiated, thepercentage of these highly sensitized candidates being transplanted Department of Medicine, Section of Nephrology, Yale University School of Medicine, New Haven, Connecticut