Estimated GFR, Albuminuria, and Physical Function: The Brain in Kidney Disease (BRINK) Cohort Study

RATIONALE & OBJECTIVE: Chronic kidney disease (CKD) is associated with impaired physical performance. However, the association between albuminuria, a marker of vascular endothelial dysfunction, and physical performance has not been fully characterized. We hypothesized that estimated glomerular filtration rate (eGFR) and albuminuria would be independently associated with physical performance. STUDY DESIGN: Cross-sectional analysis. SETTING & PARTICIPANTS: A total of 571 adults with and without CKD. PREDICTORS: Creatinine-based eGFR (eGFR(Cr)) and cystatin C-based eGFR (eGFR(CysC)) and urine albumin to creatinine ratio (UACR). OUTCOME: Short Physical Performance Battery (SPPB). ANALYTICAL APPROACH: Univariate and multivariable logistic regression models were used to examine associations of eGFR and UACR with impaired physical performance. RESULTS: Of the 571 participants (mean age, 69.3 years), 157 (27.5%) had eGFR(Cr) (mL/min/1.73m(2)) <30, 276 (48.3%) had eGFR(Cr) 30-<60, and 138 (24.2%) had eGFR(Cr) ≥60; 303 (55.3%) participants had eGFR(cysC) <30, 141 (25.7%) had eGFR(cysC) 30-<60, and 104 (19.0%) had eGFR(cysC) ≥60. Impaired physical performance was observed in 222 (38.9%) participants. Separate univariate analyses showed that lower eGFR(Cr), lower eGFR(CysC), and higher UACR were associated with higher odds of impaired physical performance. In the adjusted model with eGFR(Cr) or eGFR(CysC), UACR, and covariates, UACR retained a statistically significant association with impaired physical performance (adjusted odds ratio [OR], 2.04; 95% confidence interval [CI], 1.21-3.47 for UACR from 30-300 mg/g vs <30 mg/g and adjusted OR, 1.93; 95% CI, 1.01-3.69 for UACR >300 mg/g vs <30 mg/g), but eGFR(Cr) and eGFR(CysC) did not. LIMITATIONS: Cross-sectional analysis, estimated rather than measured GFR. CONCLUSIONS: Only UACR was associated with worse physical performance in the fully adjusted model, suggesting that vascular endothelial function and inflammation may be important mechanisms of decreased physical function. Similar results were found using eGFR(Cr) or eGFR(CysC), suggesting that confounding based on muscle mass does not explain the lack of an association between eGFR(Cr) and physical performance.