Recipient Sex Differences in Kidney Graft Survival Are Influenced by Donor Sex and Recipient Age

Objectives: An age- dependent interaction has been described for the effect of donor-recipient sex mismatch on outcomes after kidney transplant in the United States. However, this has not been verified or tested in a different cohort from another country. Materials and Methods: Data of 25 140 deceased donor kidney transplant recipients (2000-2016) were retrospectively analyzed at a population-cohort level using the United Kingdom transplant registry. Within subgroups of donor sex, associations between recipient sex and death-censored graft survival were assessed for the cohort as a whole and within recipient age subgroups. Results: No differences in graft survival were detected between female versus male recipients of male donor kidneys (adjusted hazard ratio: 1.05; P =.227). However, a significant interaction between the age and sex of recipients was identified (P =.007). Female recipients aged 25 to 44 years had significantly shorter graft survival than male recipients (adjusted hazard ratio: 1.27; P =.003), but this effect was reversed in recipients who were 45 years or older (adjusted hazard ratio: 0.94; P =.258), where there was a nonsignificant tendency for longer graft survival in females. No such effect was observed in the subgroup of female donor transplants, with no significant difference between female versus male recipients overall (adjusted hazard ratio: 1.02; P =.638) and no significant interaction with age (P =.470). Conclusions: Graft survival is influenced by the combination of recipient age and sex in recipients of male donor kidneys only. This work demonstrates findings broadly similar to published reports but presents differences in observed effect sizes among certain subgroups. Our research suggests further work is warranted to explore personalized approaches to age- and sex-adapted immunosuppression.