Sex Differences in Cause-specific Mortality in Japanese Dialysis Patients

Objective The survival advantage of females over males is lost in dialysis patients in many countries. Japanese female hemodialysis patients, however, have a survival advantage over their male counterparts. This study explored causes of death that contribute to sex differences in all-cause mortality in Japanese dialysis patients. Methods Data from the Japanese Society for Dialysis Therapy registry and National Vital Statistics from 2017 and 2018 were used. Standardized mortality ratios, male-to-female mortality rate ratios, and age-adjusted differences between sexes were calculated for all-cause, cardiovascular, and non-cardiovascular mortality, as well as cause-specific mortality, in dialysis patients and the general population. Results During the 2-year study period, 41,006 and 21,254 deaths occurred in 417,740 and 225,292 patient-years in male and female dialysis patients, respectively. The age-standardized all-cause mortality ratio was 1.21 (95% confidence interval, 1.20-1.23) for male patients compared to female patients. The male-to-female mortality rate ratio for cardiovascular disease was about 1.4 in younger age categories but closer to 1.0 in older age categories. Conversely, the ratio for non-cardiovascular disease was about 1.3 in older age categories but closer to 1.0 in younger age categories. Death from infectious disease, malignancy, and heart failure contributed to 38.4%, 22.7%, and 12.1%, respectively, of the male-to-female difference in all-cause mortality of dialysis patients. Conclusion Low cardiovascular mortality in younger age categories and low non-cardiovascular mortality in older age categories contributed to the survival advantage of female Japanese dialysis patients. Infectious disease was the greatest contributor to sex differences in all-cause mortality.