Low, rather than high, body mass index confers increased risk for post-liver transplant death and graft loss: Risk modulated by model for end-stage liver disease. 
With increasing attention being paid to optimizing patient outcomes, it has been proposed that liver transplantation (LT) for individuals with elevated body mass index (BMI) values and high Model for End-Stage Liver Disease (MELD) scores may adversely affect post-LT outcomes.  We investigated the impact of BMI on post-LT outcomes in the context of MELD at LT.  Using United Network for Organ Sharing data, we identified all adult (≥ 18 years) primary LT recipients from March 1, 2002 to September 30, 2011.  BMI categories included the following: underweight, normal, overweight, class I obese, class II obese, and class III obese (<18.5; 18.5-24.9; 25-29.9; 30-34.9; 35-39.9; ≥ 40 kg/m(2), respectively).  One-year post-LT death and graft loss were modeled using Cox regression, including interactions between BMI and MELD.  A total of 45,551 adult recipients were identified: 68% male; median (interquartile range [IQR]) age 55 years (IQR, 49-60 years); MELD, 19 (IQR, 13-26); and donor risk index, 1.39 (IQR, 1.12-1.69).  Representations in the BMI categories were underweight (n = 863, 2%), normal (n = 13,262, 29%), overweight (n = 16,329, 36%), class I obese (n = 9639, 21%), class II obese (n = 4062, 9%), and class III obese (n = 1396, 3%).  In adjusted analyses, elevated BMI was not associated with increased risk for death or graft loss.  Among the underweight, there were significant interactions between BMI and MELD with respect to death (P = 0.02) and graft loss (P = 0.01), with significantly increased risks for death (hazard ratio [HR], 1.70; 95% confidence interval [CI], 1.38-2.09; P = 0.006) and graft loss (HR, 1.45; 95% CI, 1.21-1.74; P = 0.02) among those with low MELD (≤ 26), compared to normal BMI recipients with low MELD.  In conclusion, overweight and obese LT recipients do not have increased risk of death or graft loss regardless of MELD.  Underweight patients are at increased risk for poor outcomes post-LT, specifically underweight recipients with low MELD have increased risk for death and graft loss.  Mechanisms underlying this phenomenon warrant further investigation.