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 m2) 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 m2. 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.