Sex Differences in Mortality Based on United Network for Organ Sharing Status while Awaiting Heart Transplantation

Background - There are sex differences in mortality while awaiting heart transplantation, and the reason remains unclear. Methods and Results - We included all adults in the Scientific Registry of Transplant Recipients placed on the heart transplant active waitlist from 2004 to 2015. The primary end point was all-cause mortality. Multivariable Cox proportional hazards models were performed to evaluate survival by United Network for Organ Sharing (UNOS) status at the time of listing. Random survival forest was used to identify sex interactions for the competing risk of death and transplantation. There were 33 069 patients (25% women) awaiting heart transplantation. This cohort included 7681 UNOS status 1A (26% women), 13 027 UNOS status 1B (25% women), and 12 361 UNOS status 2 (26% women). During a median follow-up of 4.3 months, 1351 women and 4052 men died. After adjusting for >20 risk factors, female sex was associated with a significant risk of death among UNOS status 1A (adjusted hazard ratio, 1.14; 95% confidence interval, 1.01-1.29) and UNOS status 1B (adjusted hazard ratio, 1.17; 95% confidence interval, 1.05-1.30). In contrast, female sex was significantly protective for time to death among UNOS status 2 (adjusted hazard ratio, 0.85; 95% confidence interval, 0.76-0.95). Sex differences in probability of transplantation were present for every UNOS status, and >20 sex interactions were identified for mortality and transplantation. Conclusions - When stratified by initial UNOS status, women had a higher mortality than men as UNOS status 1 and a lower mortality as UNOS status 2. With >20 sex interactions for mortality and transplantation, further evaluation is warranted to form a more equitable allocation system.