The Organ Procurement and Transplantation Network (OPTN) implemented a substantial redesign to the national transplant allocation system for deceased donor kidneys in December 2014. The new policies (collectively abbreviated as KAS, for “kidney allocation system”) address a number of objectives. The key goals are to make better use of available kidneys and increase transplant opportunities for difficult-to­ match patients.

United Network for Organ Sharing (UNOS), which serves as the OPTN under federal contract, is committed to sharing with the transplant community and public key metrics about how the new system is performing. At six months from system implementation, a number of trends are apparent. Key findings are summarized on the OPTN website, along with various resources to help transplant programs and candidates understand the new system.

Changes to the kidney transplant allocation system: Early observations

Some patient groups served less efficiently under the prior system have been transplanted at an accelerated rate in the first six months. Observed system performance may well be different in a few more months, or a year from now, compared to these early results, as potential “bolus effects” stabilize and as transplant centers and organ procurement organizations (OPOs) continue to adapt to the new system. Trends are being monitored closely for negative effects that may either require policy adjustment or potentially balance out over time.

Conclusions about some key metrics cannot be made until the system has been in place for a year or more. Kidney graft survival and retransplantation rates are important metrics to assess policy performance, but early data won’t reliably reflect how they may be affected by KAS.

Based on early observations, a number of outcomes are meeting policy goals. The trend that has shown the most dramatic change, although still a small subset of overall transplant numbers, is the increase in transplants among immunologically highly sensitized candidates. In the first six months since KAS implementation, candidates with a calculated panel reactive antibody (CPRA) of 99 or 100% have been transplanted at nearly six times the rate they were under the prior allocation policy. It should be noted, however, that this rate has begun to decrease. This may be an example of a bolus effect, as many highly sensitized can­didates had accumulated long wait times under the previ­ous policy (see Figure 1).


Decrease in age mismatches under new kidney allocation system

Another key anticipated outcome is a reduction in extreme age mismatches (plus or minus 15 years) between donor and recipient. While the kidney donor profile index (KDPI) and the estimated post-transplant survival (EPTS) formulas used in KAS do not rely on age alone, major mis­matches between donor and recipient age are likely to diminish the overall graft survival benefit of kidney trans­ plantation. While future data will be needed to assess the full effect on kidney outcomes, this early trend increases the likelihood of a positive effect.

Increase in African-American kidney transplant recipients

Another early and expected trend has been an increase in transplantation among African-American recipients, from approximately 32% of total transplants prior to KAS to 38% during the six-month period afterward. One new policy provision that likely has contributed to this trend is starting the waiting time calculation from dialysis/ESRD date as opposed to date of transplant center acceptance, since African-American candidates tend to be dispropor­tionately affected by delayed referral for kidney trans­ plantation. The data are also beginning to suggest a slight increase in transplants for Hispanic candidates, as well as a possible slight increase in transplants for women.

Other early trends will be closely tracked for possible unintended effects. The total number of kidney transplants has increased slightly in the first six months of KAS compared to the pre-KAS period due to an increase in the rate of kidneys recovered. The proportion of kidneys recovered for transplantation but not utilized (“discard rate”) has not fallen in the early, post-KAS period as was hoped and has actually increased slightly for high-KDPI kidneys. The OPTN/UNOS Kidney Transplantation Committee will study potential reasons affecting kidney utilization and whether the trend is likely to continue in the longer term.

Kidney transplant allocation by age

While more than half of all deceased donor kidney transplants have gone to recipients age 50 or more in the first six months of KAS, there appear to be some shifts in the number of transplants by candidate age. This was anticipated, and the magnitude of the changes will continue to be studied. Transplants have increased moderately for recipients age 18 and49 and decreased among those age 50 or older. The rate of transplantation for pediatric recipients (younger than age 18) was lower than expected in the first few months after KAS but subsequently rebounded, to the point that the six-month rate is statistically no different from the period before KAS implementation.

Kidney transplant allocation by blood type

In an effort to reduce potential biological disadvantage, KAS allows transplant programs to list candidates with blood type B to accept kidneys with a broader range of matching blood subtypes (“A2” or “A2B”). While the number of A2/A2B to B transplants performed thus far remains small, 47 of these transplants occurred in the six months since the system was implemented as compared to just six during the prior six months, a statistically significant increase. Thus far, only 4% of blood type B candidates have been registered to accept potential A2/A2B offers, suggest­ ing this aspect of the allocation system has significant unre­alized potential for broadening access to transplantation.

Increase in non-local kidney transplants

The proportion of non-local kidney transplants, those in which the donor kidney is shipped outside of the recovering OPO’s donor service area, has increased under KAS, from about one-fifth to nearly one-third of transplants. This notable increase is, in part, a byproduct of the increased access for the most difficult to match patients (those with CPRAs of 99 to 100%) and thus may eventually taper due to a bolus effect.

The OPTN will continue to review the data sys­tematically and seek the experience of the dona­tion and transplantation community to assess how the new system is performing and whether changes are needed to address significant concerns or issues. Some common issues raised by clinicians include whether older candidates have dimin­ished transplant opportunity, the impact on cold ischemic times due to more kidneys exported from their local donor service area, and the effect on patient outcomes of using higher KDPI kidneys. The OPTN will continue to closely monitor these issues.

UNOS wants feedback on new kidney transplant allocation system

No policy is ever considered “set in stone.” If you are with an The Organ Procurement and Transplantation Network (OPTN)/ United Network for Organ Sharing (UNOS) member institution, please share your experiences at a UNOS regional meeting, or contact your region’s representative to the committee (a full listing of committee members is available on the OPTN web­site. Other clinical professionals, patient advocates, and members of the public may also contact UNOS with questions or input. We welcome your feedback, ques­tions, and ideas as we continue to develop kidney alloca­tion policy that provides transplant candidates as many opportunities as possible in a fair and equitable manner.