Associations between modest reductions in kidney function and adverse outcomes in young adults: retrospective, population based cohort study

ABSTRACT: OBJECTIVE: To study age specific associations of modest reductions in estimated glomerular filtration rate (eGFR) with adverse outcomes. DESIGN: Retrospective, population based cohort study. SETTING: Linked healthcare administrative datasets in Ontario, Canada. PARTICIPANTS: Adult residents (18-65 years) with at least one outpatient eGFR value (categorized in 10 unit increments from 50 mL/min/1.73m(2) to >120 mL/min/1.73m(2)), with no history of kidney disease. MAIN OUTCOME MEASURES: eGFRs and hazard ratios of composite adverse outcome (all cause mortality, any cardiovascular event, and kidney failure) stratified by age (18-39 years, 40-49 years, and 50-65 years), and relative to age specific eGFR referents (100-110 mL/min/1.73m(2)) for ages 18-39 years, 90-100 for 40-49 years, 80-90 for 50-65 years). RESULTS: From 1 January 2008 to 31 March 2021, among 8 703 871 adults (mean age 41.3 (standard deviation 13.6) years; mean index eGFR 104.2 mL/min/1.73m(2) (standard deviation 16.1); median follow-up 9.2 years (interquartile range 5.7-11.4)), modestly reduced eGFR measurements specific to age were recorded in 18.0% of those aged 18-39, 18.8% in those aged 40-49, and 17.0% in those aged 50-65. In comparison with age specific referents, adverse outcomes were consistently higher by hazard ratio and incidence for ages 18-39 compared with older groups across all eGFR categories. For modest reductions (eGFR 70-80 mL/min/1.73m(2)), the hazard ratio for ages 18-39 years was 1.42 (95% confidence interval 1.35 to 1.49), 4.39 per 1000 person years; for ages 40-49 years was 1.13 (1.10 to 1.16), 9.61 per 1000 person years; and for ages 50-65 years was 1.08 (1.07 to 1.09), 23.4 per 1000 person years. Results persisted for each individual outcome and in many sensitivity analyses. CONCLUSIONS: Modest eGFR reductions were consistently associated with higher rates of adverse outcomes. Higher relative hazards were most prominent and occurred as early as eGFR <80 mL/min/1.73m(2) in younger adults, compared with older groups. These findings suggest a role for more frequent monitoring of kidney function in younger adults to identify individuals at risk to prevent chronic kidney disease and its complications.