The impact of sex and body mass index in liver transplantation for acute‐on‐chronic liver failure

Abstract Background/Purpose There have been no studies evaluating how body mass index (BMI) impacts on waitlist and post‐liver transplant (LT) mortality in acute‐on‐chronic liver failure (ACLF) by sex. We aimed to determine these impacts using the United Network for Organ Sharing (UNOS) database. Methods Adults listed for LT with estimated ACLF (Est‐ACLF) (2005–2023) were identified and subdivided by sex and BMI (high/middle/low). Competing‐risk analyses evaluated impacts on waitlist mortality. Kaplan–Meier analyses assessed post‐LT survival. Multivariable Cox regression identified risk factors. Results Of 37 251 Est‐ACLF patients, 14 534 (39.0%) were female. Females had higher 90‐day waitlist mortality than males (subhazard ratio [sHR]: 1.20, p < .01). High/low BMI patients had higher mortality than middle (sHR: 1.08/1.11, p < .01). In females, high BMI was associated with higher mortality than low (sHR: 1.10, p = .02); in males, low BMI was associated with higher mortality than high/middle (sHR: 1.16/1.16 vs. high/middle, p < .01). Multivariable analyses showed in females, high BMI was a significant risk factor for waitlist mortality (sHR:1.21, p < .01), while low was not; in males, high/low BMI was significant, with low having higher sHR (1.17) than high (1.09). Post‐LT survival showed no significant difference in females; in males, low BMI showed worse post‐3−/5‐year‐LT survival ( p < .01). Multivariable Cox regression showed for females, neither low nor high BMI was significant for post‐LT survival; for males, low BMI was significant for 1−/3−/5‐year‐LT survival (HR: 1.30/1.30/1.22, p < .01). Conclusions Our analysis of BMI's impact on LT outcomes in ACLF by sex enables risk stratification and provides a basis for adjusting BMI.