Mortality Prediction in the Oldest Old with Five Different Equations to Estimate Glomerular Filtration Rate: The Health and Anemia Population-based Study

BACKGROUND: Kidney function declines considerably with age, but little is known about its clinical significance in the oldest-old. OBJECTIVES: To study the association between reduced glomerular filtration rate (GFR) estimated according to five equations with mortality in the oldest-old. DESIGN: Prospective population-based study. SETTING: Municipality of Biella, Piedmont, Italy. PARTICIPANTS: 700 subjects aged 85 and older participating in the “Health and Anemia” Study in 2007–2008. MEASUREMENTS: GFR was estimated using five creatinine-based equations: the Cockcroft-Gault (C-G), Modification of Diet in Renal Disease (MDRD), MAYO Clinic, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Berlin Initiative Study-1 (BIS-1). Survival analysis was used to study mortality in subjects with reduced eGFR (<60 mL/min/1.73m(2)) compared to subjects with eGFR ≥60 mL/min/1.73m(2). RESULTS: Prevalence of reduced GFR was 90.7% with the C-G, 48.1% with MDRD, 23.3% with MAYO, 53.6% with CKD-EPI and 84.4% with BIS-1. After adjustment for confounders, two-year mortality was significantly increased in subjects with reduced eGFR using BIS-1 and C-G equations (adjusted HRs: 2.88 and 3.30, respectively). Five-year mortality was significantly increased in subjects with eGFR <60 mL/min/1.73m(2) using MAYO, CKD-EPI and, in a graduated fashion in reduced eGFR categories, MDRD. After 5 years, oldest old with an eGFR <30 mL/min/1.73m(2) showed a significantly higher risk of death whichever equation was used (adjusted HRs between 2.04 and 2.70). CONCLUSION: In the oldest old, prevalence of reduced eGFR varies noticeably depending on the equation used. In this population, risk of mortality was significantly higher for reduced GFR estimated with the BIS-1 and C-G equations over the short term. Though after five years the MDRD appeared on the whole a more consistent predictor, differences in mortality prediction among equations over the long term were less apparent. Noteworthy, subjects with a severely reduced GFR were consistently at higher risk of death regardless of the equation used to estimate GFR.