Sex differences in the survival benefit of kidney transplantation: a retrospective cohort study using target trial emulation

Abstract

Background: Kidney transplantation is the preferred treatment for eligible patients with kidney failure who need renal replacement therapy. However, it remains unclear whether the anticipated survival benefit from kidney transplantation is different for women and men.

Methods: We included all dialysis patients recorded in the Austrian Dialysis and Transplant Registry who were waitlisted for their first kidney transplant between 2000 and 2018. In order to estimate the causal effect of kidney transplantation on 10-year restricted mean survival time, we mimicked a series of controlled clinical trials and applied inverse probability of treatment and censoring weighted sequential Cox models.

Results: This study included 4408 patients (33% female) with a mean age of 52 years. Glomerulonephritis was the most common primary renal disease both in women (27%) and men (28%). Kidney transplantation led to a gain of 2.22 years (95% CI 1.88 to 2.49) compared with dialysis over a 10-year follow-up. The effect was smaller in women (1.95 years, 95% CI 1.38 to 2.41) than in men (2.35 years, 95% CI 1.92 to 2.70) due to a better survival on dialysis. Across ages the survival benefit of transplantation over a follow-up of 10 years was smaller in younger women and men and increased with age, showing a peak for both women and men aged about 60 years.

Conclusions: There were few differences in survival benefit by transplantation between females and males. Females had better survival than males on the waitlist receiving dialysis and similar survival to males after transplantation.

Keywords: kidney transplantation; renal dialysis; retrospective study; sex; survival.

Figure 1:

Flowchart describing the selection of the study cohort.

Figure 2:

Survival benefit by kidney transplantation for females and males. Upper plots show the RMST curves in years for all-cause mortality for the treatment strategies ‘remain on waitlist’ and ‘receive a transplant’ conditional on sex. The lower plot describes the survival benefit by transplantation in terms of years gained, i.e. the RMST difference between the treatment strategies ‘receive a transplant’ and ‘remain on waitlist’.

Figure 3:

Survival benefit by kidney transplantation for females and males conditional on age. Upper plots show the 10-year RMST in years for all-cause mortality for the treatment strategies ‘remain on waitlist’ and ‘receive a transplant’ for females and males conditional on age. The histograms describe the distribution of age within females and males in the auxiliary trials. The lower plot gives the survival benefit by transplantation in terms of years gained, i.e. the 10-year RMST difference between the treatment strategies ‘receive a transplant’ and ‘remain on waitlist’. Shaded areas mark pointwise 95% confidence intervals.

Figure 4:

Survival benefit by kidney transplantation for females and males conditional on time spent on waitlist. Upper plots show the 10-year RMST in years for all-cause mortality for the treatment strategies ‘remain on waitlist’ and ‘receive a transplant’ for females and males conditional on time spent on the waitlist. The histograms describe the distribution of time spent on the waitlist within females and males in the auxiliary trials. The lower plot gives the survival benefit by transplantation in terms of years gained, i.e. the 10-year RMST difference between the treatment strategies ‘receive a transplant’ and ‘remain on waitlist’. Shaded areas mark pointwise 95% confidence intervals.