Kidney Function Estimated from Cystatin C, but Not Creatinine, Is Related to Objective Tests of Physical Performance in Community-Dwelling Older Adults

Abstract

Background The burden of chronic kidney disease is highest among older adults but the significance of a diminished level of kidney function in this heterogeneous population is poorly understood. We sought to examine the relationship between estimated glomerular filtration rate (eGFR) and objective physical performance in older adults. Methods Cross-sectional analysis of 4,562 participants from The Irish Longitudinal Study on Ageing, a national cohort of community-dwelling adults aged ≥50 years. We used multivariable linear or quantile regression to model the association between categories of cystatin C (eGFR cys) or creatinine eGFR (eGFR cr) and the following outcomes: gait speed, timed-up-and-go (TUG) and grip strength. Relationships were further explored using natural eGFR splines. We examined effect modification by age in the relationship between eGFR and gait speed. Results Mean (SD) age was 61.8 (8.3) years, 53.6% were female and median (IQR) eGFR cys was 82 (70-94) mL/min/1.73m 2. In multivariable-adjusted models, participants in the lowest eGFR cys category (< 45 mL/min/1.73m 2) had 3.32 cm/s (95% confidence interval [95%CI] 0.02-6.62) slower mean gait speed, 1.32 kg (95%CI 0.20-2.44) lower mean grip strength, and 0.31 seconds (95% CI -'0.04 to 0.65) longer median TUG versus the reference group (eGFR cys ≥ 90 mL/min/1.73m 2). The relationship between eGFR cys and outcomes appeared linear but varied by age. The association between eGFR cr and outcomes tended towards a U-shape. Conclusions Cystatin C eGFR was linearly related to poorer physical performance beyond middle age among community-dwelling adults. The non-linear relationships observed with eGFR cr underscore the limitations of creatinine as a predictor of frailty outcomes in older individuals.