Inequity in organ allocation for patients awaiting liver transplantation: Rationale for uncapping the model for end-stage liver disease

Abstract

Background & aim: The goal of organ allocation is to distribute a scarce resource equitably to the sickest patients. In the United States, the Model for End-stage Liver Disease (MELD) is used to allocate livers for transplantation. Patients with greater MELD scores are at greater risk of death on the waitlist and are prioritized for liver transplant (LT). The MELD is capped at 40 however, and patients with calculated MELD scores >40 are not prioritized despite increased mortality. We aimed to evaluate waitlist and post-transplant survival stratified by MELD to determine outcomes in patients with MELD >40.

Methods: Using United Network for Organ Sharing data, we identified patients listed for LT from February 2002 through to December 2012. Waitlist candidates with MELD ⩾40 were followed for 30days or until the earliest occurrence of death or transplant.

Results: Of 65,776 waitlisted patients, 3.3% had MELD ⩾40 at registration, and an additional 7.3% had MELD scores increase to ⩾40 after waitlist registration. A total of 30,369 (46.2%) underwent LT, of which 2,615 (8.6%) had MELD ⩾40 at transplant. Compared to MELD 40, the hazard ratio of death within 30days of registration was 1.4 (95% CI 1.2-1.6) for patients with MELD 41-44, 2.6 (95% CI 2.1-3.1) for MELD 45-49, and 5.0 (95% CI 4.1-6.1) for MELD ⩾50. There was no difference in 1- and 3-year survival for patients transplanted with MELD >40 compared to MELD=40. A survival benefit associated with LT was seen as MELD increased above 40.

Conclusions: Patients with MELD >40 have significantly greater waitlist mortality but comparable post-transplant outcomes to patients with MELD=40 and, therefore, should be given priority for LT. Uncapping the MELD will allow more equitable organ distribution aligned with the principle of prioritizing patients most in need. Lay summary: In the United States (US), organs for liver transplantation are allocated by an objective scoring system called the Model for End-stage Liver Disease (MELD), which aims to prioritize the sickest patients for transplant. The greater the MELD score, the greater the mortality without liver transplant. The MELD score, however, is artificially capped at 40 and thus actually disadvantages the sickest patients with end-stage liver disease. Analysis of the data advocates uncapping the MELD score to appropriately prioritize the patients most in need of a liver transplant.

Keywords: Liver allocation; Liver transplantation; Model for end-stage liver disease (MELD); Post-transplant outcome; Regional disparity; Share 35; Waitlist mortality.

Fig. 1.. Number of adult deceased donor liver transplants with Model for End-stage Liver Disease (MELD) ⩾40.

MELD score was implemented February 27^th, 2002. Data from Organ Procurement and Transplantation Network (OPTN) as of May 31, 2015 (http://optn.transplant.hrsa.gov). The dashed vertical line marks the implementation of Share 35.

Fig. 2.. Percentage of adult deceased donor liver transplants with Model for End-stage Liver Disease (MELD) ⩾40 and median MELD at time of transplantation in Each Organ Procurement and Transplantation Network (OPTN) region from March 1, 2002 through December 31, 2015. (http://optn.transplant.hrsa.gov).

States in each OPTN Region (# of adult liver transplant centers): Region 1: Connecticut (2), Massachusetts (4), Maine (0), New Hampshire (0), Rhode Island (0), Vermont (0); Region 2: District of Columbia (1), Maryland (2), New Jersey (2), Pennsylvania (10), Delaware (0), West Virginia (0); Region 3: Alabama (1), Arkansas (1), Florida (7), Georgia (2), Louisiana (3), Mississippi (1), Puerto Rico (1); Region 4: Oklahoma (2), Texas (10); Region 5: Arizona (4), California (9), Utah (2), Nevada (0), New Mexico (0); Region 6: Hawaii (1), Oregon (3), Washington (2), Alaska (0), Idaho (0), Montana (0); Region 7: Illinois (5), Minnesota (3), Wisconsin (3), North Dakota (0), South Dakota (0); Region 8: Colorado (3), Iowa (1), Kansas (1), Missouri (3), Nebraska (1), Wyoming (0); Region 9: New York (7), Vermont (0); Region 10: Indiana (1), Michigan (3), Ohio (4); Region 11: Kentucky (2), North Carolina (3), South Carolina (1), Tennessee (2), Virginia (2).

Fig. 3.. Flow diagram of the cohort of patients included in the study.

Fig. 4.. Model for End-Stage Liver Disease (MELD) score for patients waiting for LT and relative risk of death.

Cox regression analysis, with MELD as a time-dependent covariate, was used to estimate the hazard ratio (HR) of death for patients according to their MELD score at each time point, all compared to the corresponding group of patients with MELD = 40. Smoothing splines were used to illustrate the relative risk of death of patients with different MELD scores.

Fig. 5.. Kaplan-Meier overall patient survival estimates at (A) 30 days from waitlist registration among patients with Model for End-Stage Liver Disease (MELD) ⩾40 at time of waitlist registration, (B) 30 days from first MELD ⩾40 among patients whose MELD reached ⩾40 on waitlist at anytime and (C) 3 years post liver transplantation.

The overall survival and post-transplant survival probabilities were calculated using the Kaplan-Meier method with Greenwood standard errors. p values were based on log-rank trend tests.