Our study describes the U.S. experience with national sharing of livers for transplantation. We confirmed that donors of nationally compared to locally placed livers were of lower quality with respect to donor characteristics including age, African-American race, height, positive HCV-antibody, CDC high risk classification, cause of death and donation after cardiac death. However, after adjusting for these differences in donor quality—in addition to significant recipient characteristics and center/geographic effects-–we found that transplantation with a nationally placed liver was associated with no increased risk of patient and graft loss compared to transplantation with a locally placed liver.
Surprisingly, we found that utilization of nationally offered livers was highly concentrated among six centers in the United States, while 43 (38%) centers did not accept a single nationally offered liver. The majority of these high-utilizing centers were high-volume centers located in DSAs with greater center competition and high median LT-MELD scores. On average, nationally placed livers accounted for nearly one-quarter of the total adult transplant volume at each of these centers. This distribution pattern is certainly unexpected in the context of the current MELD allocation policy that is based on the disease severity of individual candidates. These data strongly suggest that factors other than pure donor and recipient variables influence the decision to accept a nationally offered liver. Moreover, the heavy concentration of nationally placed livers in a few centers suggests the existence of expedited placement pathways leading to a small number of transplant centers. Current OPTN policy does not include an overt mechanism of expedited organ placement so these placements are presumably being done on an ad hoc basis.
Our data also revealed that one quarter of national liver recipients had an LT-MELD <15, the threshold below which patients may not derive overall liver transplant survival benefit from deceased donors (6
). This threshold for survival benefit was adjusted for average
donor quality, so it is possible that this LT-MELD threshold would be even higher for patients accepting a lower quality, nationally distributed liver. Although these patients with a lower LT-MELD score may have fallen into the subgroup of patients who are underserved by the MELD estimation of waitlist mortality (7
), we did not find evidence that these patients were sicker based on the available data related to encephalopathy, ascites, serum sodium or albumin, as collected in the UNOS/OPTN registry.
The reason why these patients with lower LT-MELD scores received these lower quality, nationally distributed livers rather than higher LT-MELD patients on the local, regional, or national waitlists is unknown. The accepting center may determine that the patient is at significant risk of death that is not reflected by his/her MELD score (such as an HCC patient beyond Milan). A less charitable scenario is that the center may transplant these low MELD patients with a national liver reserving their higher MELD patients to compete with patients at other local centers for local organs. This is supported by our data revealing that fewer recipients of nationally distributed livers were listed with HCC and non-HCC exceptions, as these patients otherwise have access to deceased donor livers at higher LT-MELD scores through predictable MELD increases.
One might have expected that nationally distributed livers—declined on both the local and regional levels, presumably for reasons of donor quality—would be associated with significantly higher rates of patient and graft loss. However, recent data have shown that centers transplanting a higher volume, as defined as >78 transplants per year, had improved graft survival with high-DRI livers compared to low volume centers (5
). We speculate that the centers that utilize a high volume of nationally offered livers have greater experience with managing the immediate and long-term complications associated with high-DRI livers. A future study looking specifically at the association between the volume of nationally distributed livers and center-specific survival is planned to better understand our findings.
We acknowledge that there are limitations to our study. Administrative datasets are subject to entry error or inconsistencies with respect to subjective variables such as ascites or encephalopathy. By combining the categories of “moderate” and “severe” for these two variables, we attempted to capture simply the “presence” versus “absence” of these characteristics, which is less subject to error. In addition, some aspects of a recipient’s clinical status that may prompt a clinician to accept a national liver despite low prioritization by the LT-MELD, such as functional well-being and life-limiting symptoms related to liver disease, are not captured by the registry. Lastly, statistically significant differences between groups may, in fact, be an artifact of the large sample size, warranting caution when interpreting data especially with respect to the overall ‘health’ of national versus local liver recipients.
Despite these limitations, evaluation of national liver allocation and distribution could not have been performed without the use of the UNOS/OPTN registry, and our results have important implications for the U.S. liver distribution system. Currently, livers are allocated locally, regionally, then nationally, based on arbitrary geographic boundaries. Centers located in regions covering a small geographic area may better be able to utilize a nationally distributed liver with less cold ischemia time than centers in larger regions. As a purely hypothetical example, a center in Tennessee (UNOS region 11) can accept a nationally offered liver from centers in UNOS regions 2, 3, 4, 7, 8 and 10 with a transport distance shorter than that of a regionally offered liver travelling from Albuquerque, New Mexico, to San Francisco, California. Our data, demonstrating that nationally distributed livers have no increased risk of graft loss compared to a liver with similar donor characteristics, argue for the elimination of the arbitrary geographic DSA and UNOS region boundaries in favor of expanded sharing agreements over broader geographic areas. Alternatively, given the high concentration of nationally distributed livers within a few centers, expedited liver graft placement to centers that are experienced with utilizing these lower quality livers in a more transparent and formalized fashion may help to streamline the donor offer process.
In conclusion, our study is the first to shed light on the highly concentrated distribution of nationally placed livers. Let this be the foundation for an informed discussion about changing our current liver allocation and distribution policies.