OBJECTIVE

To determine the distribution of kidney function values as measured by glomerular filtration rate (GFR), and the rate of decline with age in male and female healthy subjects without pre-existing medical conditions.

DESIGN

Systematic review and structured synthesis.

SEARCH SOURCES

PubMed, Embase, Cochrane Central Register of Controlled Trials and Web of Science, from database inception to 25 October 2023. Unpublished studies were searched from clinical trial registries and the grey literature.

SELECTION CRITERIA

Observational cohort studies, including non-treatment arms of randomised, pseudorandomised and non-randomised controlled trials that assessed the age-related decline in kidney function over time.

MAIN OUTCOME MEASURES

Primary outcomes were rate of change of kidney function over time (absolute and relative change) and rate of change of kidney function with age. Secondary outcomes included rate of change of kidney function compared with baseline GFR, gender, ethnicity and proportion of participants >60 years defined as having chronic kidney disease.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened studies for inclusion, extracted data and assessed risk of bias. Data could not be pooled because of significant heterogeneity. Instead, a descriptive analysis was used to synthesise results.

RESULTS

12 studies between 1958 and 2021 reported the decline rate of kidney function in healthy individuals: six prospective cohort studies, four retrospective cohort studies and two randomised controlled clinical trials, which included 129 359 healthy participants (range from 15 to 46 682) and ranged from 2 to 23 years duration. Annual decline rates ranged from -0.24 to -3.60 mL/min/1.73 m/year (-0.37 to -1.07 in subjects without hypertension). Results were mixed as to whether decline rates sped up or slowed down with age, and whether decline rates differed between women and men, with studies showing conflicting results. This study was unable to determine the decline rates in different ethnicities.

CONCLUSIONS

This study is the first systematic review to investigate the longitudinal decline in kidney function with age in healthy individuals. The normal decline rate could be considered between -0.37 and -1.07 mL/min/1.73 m/year in healthy adults without hypertension. Kidney function decline rates in healthy adults may be helpful to clinicians anticipating patients' kidney trajectory and determining whether chronic kidney disease-specific care is required.

PROSPERO REGISTRATION NUMBER

CRD42023096888.