Fast-tracking and fairness: Getting organ offers quickly to candidates who will accept them

Authors

  • Sommer E. Gentry,

    Corresponding author
    1. Department of Mathematics, US Naval Academy, Annapolis, MD
    • Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD
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  • Dorry L. Segev

    1. Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD
    2. Department of Epidemiology, Johns Hopkins School of Public Health, Baltimore, MD
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  • See Article on Page 404

Address reprint requests to Sommer E. Gentry, Ph.D., Department of Mathematics, US Naval Academy, 572-C Holloway Road, Mail Stop 9E, Annapolis, MD 21402. Telephone: 410-293-6724; E-mail: gentry@usna.edu

In this issue of Liver Transplantation, Lai et al.[1] present compelling evidence that many nationally offered livers are placed through expedited pathways that could bypass higher priority candidates. Because transplant centers vary widely in their propensity to accept lower quality livers,[2] it is certainly plausible that some organ procurement organizations make fast-track offers to centers that they believe are most likely to accept a given lower quality liver. Although this practice is clearly motivated by the desire to make the most effective use of the organ supply, the design of expedited placement arguably falls under the jurisdiction of the Organ Procurement and Transplantation Network because of the equity considerations that arise.

In order to get livers as quickly and efficiently as possible to the highest priority candidates who will accept them, some lessons can be adapted from recent changes to the distribution of kidneys. DonorNet 2007 was implemented with the stated goals of facilitating and expediting organ placement by requiring offers to be made to candidates in the order specified by the national match run list; at the regional and national levels, it permitted simultaneous offers to a limited number of centers. However, the distribution of kidneys among centers became no more equitable (the confidence interval for the change in the Gini coefficient was −0.016 to 0.036), the discard rate increased by 13%, and those kidneys that already had the longest cold ischemia times incurred an additional 5 to 25 hours of cold ischemia.[3] It turns out that offering organs in precisely the order dictated by a national list makes the placement of the hardest-to-place kidneys even less efficient and no more equitable.

Lai et al.[1] propose an elegant solution: once a liver has been refused at local and regional levels, it should be simultaneously offered to every transplant center that chooses to entertain national offers. Each center would specify its highest allocation priority candidate for whom it would accept the offer, and the liver would be allocated to the highest allocation priority candidate among all the centers. In their proposed system, transplant centers could either opt out of national offers entirely or receive every national offer.

With such a system, one foreseeable issue is the offer burden. Not all national offer livers are the same, and the range of suboptimal livers that centers are willing to transplant is quite wide in terms of both the degrees of certain parameters (eg, age) and the category of risk (eg, infectious risk versus steatotic risk).[2] A center might be loathe to entertain hundreds of national offers just to find 1 liver within its predefined criteria, so centers should have the ability to specify acceptance criteria on a center level as well as a candidate level (some candidates may be more appropriate for risky organs than others).

Unfortunately, the current system for specifying acceptance criteria seems inadequate, and this is another lesson that can be adapted from the kidney experience. UNet includes kidney donor acceptance criteria and allows centers to specify maximum ischemia times, minimum and maximum donor weights, minimum and maximum donor ages, and several other univariate donor criteria for each candidate. However, nearly all centers adopt identical criteria for all candidates and, furthermore, specify criteria that are much broader than the parameters of kidney offers that these centers have actually accepted.[4] For instance, some centers have specified an age maximum that is decades older than the age of their oldest accepted kidney offers. It is likely that the univariate nature of the current system fails to capture the complexity of organ decision making and that this process either is inherently too complex to capture electronically or just requires a more sophisticated system. Regardless of the reasons, this poor utilization of the current acceptance criteria system causes thousands of surplus offers: 7.1% of all kidney offers had parameters that were more extreme than the maximum parameters of kidneys actually transplanted at centers over a decade, and this represents a substantial ongoing offer burden.

There are 2 steps to expediting the placement of hard-to-place organs and reducing discards without disadvantaging any candidate. First, we must discover which organs are hard to place. Second, we must design efficient, equitable distribution systems to get those hard-to-place organs to the highest priority candidates and centers that will use them. In the context of kidneys, the probability of discard or delay model can identify hard-to-place organs and might be extended to livers.[5] Predicting the probability of delay or discard must be distinguished from predicting worse transplant outcomes because there are factors not necessarily associated with worse outcomes in a population-based regression model (eg, Centers for Disease Control and Prevention high-risk donors) that in fact are associated with organ acceptance behavior. It is, therefore, inadequate to use a donor risk index based on predicted outcomes as a surrogate here. In liver transplantation, if the offers are made before organ recovery and the donor is hemodynamically stable, time is likely less of the essence in comparison with kidneys, which are usually offered ex vivo; as such, it may be that “declined by all centers in the region” can serve as an adequate surrogate for hard-to-place organs. The experience in kidney distribution also supports the need for the second step (efficient distribution): according to the probability of discard or delay, 40% of centers did not transplant a single hard-to-place kidney over a 4-year period, whereas only 16% of centers transplanted more than 2 hard-to-place kidneys per year.[5]

Because hard-to-place organs are destined to be refused by many candidates at many centers, the distribution of these organs must somehow be expedited. As Lai et al.[1] point out, the current system of expediting is ad hoc and possibly unfair. A new system is needed, but care must be taken to avoid the unintended side effect of increasing discards, as occurred in kidney transplantation, because every lost transplant opportunity is unfair to all concerned.

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