To whom goes the kidney?

Deceased donor organs in the United States continue to be a scarce resource, and the debate over the equity of kidney allocation to liver transplant candidates with renal insufficiency remains unresolved. The increasing prevalence of acute and chronic renal dysfunction among liver transplant candidates across the backdrop of an ever-growing kidney transplant waiting list has created and continues to create a set of competing priorities and a seemingly circular debate about how best to optimize a scare resource. In one corner are data demonstrating increased waiting-list mortality among end-stage liver disease patients with comorbid renal disease; this suggests that simultaneous liver-kidney transplantation (SLK) should be the norm for liver candidates with renal impairment. In the other corner are data suggesting that upward of 80% of liver transplant recipients on renal replacement therapy (RRT) for fewer than 30 days go on to recover renal function after transplantation, and this indicates that at least some kidneys transplanted as part of SLK are unnecessary. To whom then goes the kidney, the liver transplant candidate with renal impairment or the kidney transplant candidate? There is little debate about the necessity for SLK among end-stage renal disease patients with decompensated cirrhosis because these patients have no hope of recovering renal function and would not survive kidney transplantation alone; this establishes a clear role for SLK. Therefore, how we frame the discussion about SLK is critical. The debate is not whether to eliminate SLK; rather, the focus of the debate should be the subset of liver transplant candidates with recent renal impairment (<90 days). The debate then seeks to answer the question of whether the addition of a kidney transplant, among this subset of patients, is associated with a survival benefit. In this month’s issue of Liver Transplantation, Chang et al. attempt to address this question by using Markov modeling to compare the effectiveness of SLK, liver transplantation alone (LTA) with subsequent kidney transplantation if needed (the current kidney allocation system), and LTA with subsequent kidney transplantation if needed (16-week wait time) among liver transplant candidates on RRT. The authors conclude that SLK is associated with the best shortand long-term survival among liver transplant candidates receiving pretransplant RRT. This benefit appears to be independent of the Model for End-Stage Liver Disease and the length of time on RRT. Although these results add to the debate, they do not definitively answer the question at hand. As in other studies, the survival benefit analysis fails to account for the kidney transplant candidates who lose an opportunity for transplant each time that a kidney is allocated as part of SLK. Wait-list mortality among kidney transplant candidates is high and ranges from 6% to 15% per year. In the context of the organ shortage, a debate about the survival benefit of kidney transplantation for liver transplant candidates cannot occur without accounting for the 100,000 people waiting for kidney transplantation alone. Results from the current study demonstrate a 5.5% survival benefit of SLK versus LTA with subsequent kidney transplantation if needed (16-week wait time) among liver candidates on RRT for fewer than 30 days and a 17% survival benefit among liver candidates on RRT between 60 and 90 days. These estimated survival benefits do not exceed the annual wait-list mortality among kidney transplant candidates and, moreover, are likely inflated because they do not account for the