The new kidney allocation system (KAS) began December 2014.  As previously blogged, key strategic goals of the KAS include more equity for highly sensitized patients, minorities, and blood group B recipients, as well as improving donor kidney/recipient longevity matching.  To achieve these goals, KAS introduced two new terms (estimated post transplant survival [EPTS] and kidney donor profile index [KDPI]) and created rules that increase mandatory organ sharing for highly sensitized patients and for donor kidneys with a KDPI score > 85 (high KDPI kidneys).

Several sessions of the ATC were dedicated to updates on KAS from the United Network for Organ Sharing (UNOS).  Dr. Aeder, chair of the kidney committee, discussed the impact of the KAS on longevity matching.  With KAS kidneys with KDPI < 20% (the kidneys expected to last the longest) are preferentially allocated to pediatric recipients and recipients with an EPTS score < 20 (the patients expected to live the longest).  However certain patients–multiorgan, prior living donors and highly sensitized patients–can be allocated without the use of KDPI and EPTS scores.  UNOS  analyzed data on allocation of low KDPI kidneys from June 2013 – December 2014 (pre KAS) to December 2014 – August 2015 (post KAS).  During both the pre- and post-KAS period, about 22% of low KDPI kidneys were allocated to multiorgan recipients.  In the pre- and post-KAS periods, respectively, 28% and 53% of these low KDPI kidneys went to pediatric or low EPTS patients.  Highly sensitized patients received 13.8% of low KDPI kidneys post KAS compared to 2.1% pre KAS.  The majority of these highly sensitized patients (11.2%) had EPTS scores > 20%.   In both the pre- and post-KAS period, prior living donors accounted for <1% of low KDPI transplants.  A reported 2.4% of low KDPI kidneys were discarded post KAS while 2.6% were discarded pre KAS.  Overall, it appears that longevity matching has improved after the implementation of KAS.  However, a large number of the “best” kidneys do go to multiorgan transplant recipients, in whom the EPTS and reported outcomes were not discussed.   In addition, several ATC audience members worried that placing these kidneys in highly sensitized patients will put them at higher risk of failure.  It is likely, however, that the “bolus effect” in transplanting highly sensitized patients, will result in a decrease in the use of low KDPI kidneys for highly sensitized patients over time.  This will likely be debated for several years until we have enough data to compare patient and graft survival in the pre- and post-KAS periods.

The second presentation by Darren Stewart from UNOS was about discard rates pre and post KAS.  Discard rates increased from 18.3% to 20.2% during the first 7 months of KAS implementation, but in the subsequent 4 months, this rate returned to 17.9%.  At the same time, deceased donor transplant volume is up 4.6%.  The study aimed to understand the changes in discard rate. Organ Procurement and Transplantation Network data were used to analyze and determine which factors affected the discard rate in the pre-KAS period vs post-KAS period.  Interestingly, investigators found that the increase of discards could be explained by poor biopsy findings and a decline in pumping kidneys.  Sharing kidneys for highly sensitized patients and regional sharing of high KDPI kidneys did not impact discard rates.  However, it is possible that changes in pumping kidney practices could have been impacted by increased regional sharing as a result of KAS.  Moving forward, this is a topic that will be closely monitored and discussed, as reducing discard rates is a priority in allocation.

Post by Dr. Vinay Nair, AJKD Blog Advisory Board member.

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