Frailty, a geriatric syndrome marked by reduced physiological reserves, has been linked to organ dysfunction. However, the specific contribution of kidney function to frailty remains underexplored. This study aims to assess the impact of kidney function on frailty in a large population of older adults.

The FRASNET cohort, including elderly, non hospitalized individuals, was evaluated for frailty, markers of kidney, glomerular, and tubular function, and for anthropometric parameters.

We included 1183 individuals in this study (59.9% females, age 65–93). Among them, 27.7% of subjects were classified as robust, 37.6% were pre-frail, and 34.7% were frail. The prevalence of frailty increased with age (43% in individuals over 76 years of age) and was associated with obesity (28.3%) and polytherapy (23.2%). Whole estimated glomerular filtration rate (eGFR) was 73.8 (IQR 62.4, 84.7) ml/min/1.73 m2. The prevalence of chronic kidney disease (CKD) increased across frailty classes from 15.2% in robust to 29.0% in frail individuals (P < 0.001). Among young-old subjects (65–75 years old), comorbidity was the main determinant of frailty, whereas in older subjects, when eGFR was below 53.5 ml/min/1.73 m2, it was associated with frailty (P < 0.002). Fractional excretion of sodium progressively increased across frailty classes, from 0.71% in robust individuals (IQR 0.46–1.03) to 0.79% in frail subjects (IQR 0.48–1.17) (P = 0.04).

This study revealed a strong relationship between CKD and frailty, identifying a new eGFR threshold associated with frailty in older adults. The alterations in age- and frailty-dependent sodium handling highlight the potential role of the often-overlooked tubular function in older individuals.