Sex differences in mortality among binational cohort of people with chronic kidney disease: population based data linkage study

Abstract

Objective: To evaluate sex differences in mortality among people with kidney failure compared with the general population.

Design: Population based cohort study using data linkage.

Setting: The Australian and New Zealand Dialysis and Transplant Registry (ANZDATA), which includes all patients receiving kidney replacement therapy in Australia (1980-2019) and New Zealand (1988-2019). Data were linked to national death registers to determine deaths and their causes, with additional details obtained from ANZDATA.

Participants: Of 82 844 people with kidney failure, 33 329 were female (40%) and 49 555 were male (60%); 49 376 deaths (20 099 in female patients; 29 277 in male patients) were recorded over a total of 536 602 person years of follow-up.

Main outcome measures: Relative measures of survival, including standardised mortality ratios, relative survival, and years of life lost, using general population data to account for background mortality (adjusting for country, age, sex, and year). Estimates were stratified by dialysis modality (haemodialysis or peritoneal dialysis) and for the subpopulation of kidney transplant recipients.

Results: Few differences in outcomes were found between male and female patients with kidney failure. However, compared with the general population, female patients with kidney failure had greater excess all cause deaths than male patients (female patients: standardised mortality ratio 11.3, 95% confidence interval 11.2 to 11.5, expected deaths 1781, observed deaths 20 099; male patients: 6.9, 6.8 to 6.9, expected deaths 4272, observed deaths 29 277). The greatest difference was observed among younger patients and those who died from cardiovascular disease. Relative survival was also consistently lower in female patients, with adjusted excess mortality 11% higher (95% confidence interval 8% to 13%). Average years of life lost was 3.6 years (95% confidence interval 3.6 to 3.7) greater in female patients with kidney failure compared with male patients across all ages. No major differences were found in mortality by sex for haemodialysis or peritoneal dialysis. Kidney transplantation reduced but did not entirely remove the sex difference in excess mortality, with similar relative survival (P=0.83) and years of life lost difference reduced to 2.3 years (95% confidence interval 2.2 to 2.3) between female and male patients.

Conclusions: Compared with the general population, female patients had greater excess deaths, worse relative survival, and more years of life lost than male patients, however kidney transplantation reduced these differences. Future research should investigate whether systematic differences exist in access to care and possible strategies to mitigate excess mortality among female patients.

Fig 1

Leading causes of death in patients receiving kidney replacement therapy in Australia and New Zealand by sex and age at death. See appendix table 1 for other causes of death by sex and appendix table 2 for absolute counts by sex

Fig 2

Percentage of deaths by cause in patients receiving kidney replacement therapy in Australia and New Zealand over time, 1988-2017 (Lowess lines are used). See appendix table 1 for other causes of death by sex and appendix table 2 for absolute counts by sex

Fig 3

Estimates of mortality rates by age and sex (upper panel) and standardised mortality ratios by age and sex (lower panel) for patients receiving kidney replacement therapy in Australia and New Zealand

Fig 4

Standardised mortality ratios by calendar year (with Lowess fitted line; upper panel) and by cause of death (lower panel) for patients receiving kidney replacement therapy in Australia and New Zealand

Fig 5

Survival in population receiving kidney replacement therapy relative to matched general population (relative survival) in Australia and New Zealand by sex and time since start of kidney replacement therapy (upper panel) and first kidney transplant (lower panel)

Fig 6

Expected life years lost by sex and age at start of kidney replacement therapy (upper panel) and first kidney transplant (lower panel). Age represents five year age band except where indicated otherwise