Summary
A retrospective analysis of US transplant registry data found sex-associated differences in donor-heart sizing and treated rejection across the transplant pathway. The medRxiv preprint found no significant change across eras in the short-term survival difference between women and men.
A retrospective study linking US heart-transplant registry and donor-offer records found that sex-associated differences appeared at several stages of the transplant pathway, but did not all point in the same direction. Women had fewer severely undersized donor hearts among realized offers and more treated rejection after transplant; adjusted one-year survival was similar, and the survival difference did not change significantly between the study’s pre- and post-2018 eras.
The study, posted as a medRxiv preprint on October 24, 2026, analysed 51,970 listing episodes, 1,388,553 actual donor offers and 38,417 transplant recipients. It linked UNOS STAR candidate, donor, transplant and match-run data. The analysis was retrospective and observational, rather than a trial assigning treatments or donor hearts.
Differences along the offer pathway
Transplant access increased for both sexes across the two eras, with no evidence that the change differed by sex (sex-by-era interaction P=.133). Among offers made to candidates, adjusted conditional probabilities of final acceptance were higher for female candidates in both eras. The study found no evidence that this sex difference in acceptance changed across eras (interaction P=.172).
The researchers also examined donor-heart size using predicted heart mass (PHM), a measure used to assess the fit between a donor heart and a recipient. After standardizing for recipient size, severe PHM undersizing—defined in the study as a ratio below 0.86—was less frequent among realized offers for women than for men. It occurred in 28.9% of offers for women and 38.3% for men before 2018, and in 25.5% and 35.4%, respectively, after 2018.
The researchers found no evidence that undersized offers were accepted at a lower rate for female candidates than for male candidates (three-way interaction P=.800). This pattern means the difference in the size of hearts that reached recipients was already visible among realized offers, rather than being explained solely by lower acceptance of undersized offers for women.
Rejection and one-year survival
Treated rejection after transplant remained more common among women in adjusted analyses. The male-versus-female odds ratio was 0.667 (95% CI, 0.589–0.756). After adjustment for calculated panel-reactive antibody (cPRA) in the post-2018 era, the male-versus-female odds ratio was 0.678 (95% CI, 0.583–0.790).
For the post-2018 era, adjusted 365-day survival was 91.0% among women and 92.3% among men. The estimated change in the sex difference across eras was −0.64 percentage points (95% CI, −1.97 to 0.68; P=.341), which was not statistically significant. The findings therefore describe distinct patterns in offers, matching and post-transplant outcomes; they do not identify a single explanation for those differences.
Because this is a retrospective registry study and is currently a preprint, its findings are observational and should be interpreted as such. The authors’ central point is that transplant performance is best assessed at multiple stages—from donor-offer exposure and acceptance through matching and outcomes—rather than by survival alone.