The role of cystatin-C in the confirmation of reduced glomerular filtration rate among the oldest old

INTRODUCTION: Current guidelines suggest using cystatin-C to confirm a reduced creatinine-based estimated glomerular filtration rate (eGFR(cr)) when the latter is thought to be inaccurate. Older adults have reduced muscle mass, which may affect the accuracy of eGFR(cr). We evaluated the use of cystatin-C-based eGFR (eGFR(cys)) to confirm reduced eGFR(cr) among adults ≥ 80 years of age and, for comparison, younger adults. MATERIAL AND METHODS: We analyzed data from 3,059 REasons for Geographic And Racial Differences in Stroke (REGARDS) study participants with reduced eGFR(cr) (< 60 ml/min/1.73 m(2)) enrolled in 2003–2007 who were not on dialysis. eGFR(cr) and eGFR(cys) were calculated using age, sex and race-adjusted equations. Confirmed reduced eGFR(cr) was defined as eGFR(cys) < 60 ml/min/1.73 m(2). Prevalence of chronic kidney disease complications at baseline and all-cause mortality up to March 2012 were calculated. Analyses were stratified by age: < 65, 65–79 and ≥ 80 years. RESULTS: Among participants < 65, 65–79 and ≥ 80 years of age, 76.5%, 85.7% and 92.5%, respectively, had reduced eGFR(cr) confirmed with eGFR(cys) (p < 0.001). Among participants ≥ 80 years of age, those with reduced eGFR(cr) confirmed with eGFR(cys) had higher prevalence of hypertension (79.1% vs. 65.1%, p = 0.03) and albuminuria (38.3% vs. 22.7%, p = 0.04) and higher risk for all-cause mortality (hazard ratio: 2.43; 95% confidence interval: 1.19–5.01) as compared with those in whom reduced eGFR(cr) was not confirmed by eGFR(cys). CONCLUSIONS: Reduced eGFR(cr) was confirmed using eGFR(cys) for the vast majority of adults ≥ 80 years. These results suggest that using cystatin-C to confirm a reduced eGFR(cr) may not be necessary among the oldest old.