Albuminuria: A Novel Marker for Functional Impairment in Older Adults?

Previous studies have well-characterized the association between advanced renal impairment and decline in functional status, particularly in the end-stage renal disease population [4] . However, few studies have examined this relationship at earlier stages of chronic kidney disease (CKD) or attempted to incorporate albuminuria into the assessment. Recently, Bowling et al. [5] examined fall risk in a cohort of 8,744 adults (including 1,604 adults with CKD) from the Reasons for Geographic and Racial Differences in Stroke study. Similar to the Wolfgram study, decline in eGFR was not associated with increased risk for serious fall injury, whereas fall risk increased with progressively higher category of albuminuria. Together, the findings from the Bowling and Wolfgram studies suggest that albuminuria may be more sensitive than eGFR in identifying patients at risk for functional impairment, at least in patients with earlier stages of CKD. The findings from these studies are both congruent and complementary. While the Bowling study focused on the hard outcome of serious fall-related injury, the Wolfgram study examined surrogates for functional impairment. The latter finding is particularly important because it lends support to the ability to identify a signal for fall risk before an actual event. Falls and fallrelated injuries are highly prevalent and potentially devastating complications in older adults [6] , and patients with CKD are at particularly high risk [5] . The ability to identify patients at risk at an early stage – when preventative interventions are most likely to be effective – is therefore an important public health goal. Over the past 2 decades, the clinical significance of albuminuria has been increasingly recognized, most notably as an independent predictor of adverse cardiovascular and renal outcomes [1, 2] . The kidneys can thus be regarded as providing a window on systemic endothelial function, with urinary albumin being a sensitive, inexpensive, and widely available lens through which vascular health can be gauged. Now, there may be even more reason to pay close attention to urinary albumin excretion. In this issue of the American Journal of Nephrology , Wolfgram et al. [3] present a secondary analysis from the Systolic Blood Pressure Intervention Trial (SPRINT). Using a subgroup of adults aged 75 years or older, they examined data from the baseline study assessment period. In addition to renal indices (estimated glomerular filtration rate [eGFR] and albuminuria), participants in this subgroup underwent functional performance evaluation using 3 different validated tools: (1) gait speed assessment, (2) a self-administered health-related quality of life survey focusing on functional status (EuroQol 5 dimensions questionnaire [EQ-5D]), and (3) a self-administered fall risk assessment tool (Falls Efficacy Scale [FES]). In unadjusted modeling, both decreasing eGFR and increasing albuminuria categories were associated with worse scores on the 3 performance outcome measures. In adjusted models (including adjustment for albuminuria), eGFR was no longer a significant predictor of performance scoring. However, albuminuria remained a significant predictor for both gait speed and EQ-5D, although not for FES scoring. Published online: January 21, 2017 Nephrology American Journal of