Renal function in community-dwelling frail elderly.: Comparison between measured and predicted glomerular filtration rate in the elderly and proposal for a new cystatin C-based prediction equation

Background and aims: There is a great need to evaluate renal function regularly in elderly people. This study aimed at analyzing renal function in stable, community-dwelling elderly people of 75 years and over, to compare measured and predicted glomerular filtration rates (GFR) and to develop an accurate prediction equation for this age group. Methods: Forty-five ambulatory elderly people in stable health in ordinary living were randomly selected into four age-classes, aged 75-95. Demographic data, personal activities of daily living, continuous drug prescriptions, body composition, blood pressure and blood chemistry were analysed. GFR was measured as Iohexol clearance based on three time-points 3, 4 and 7 hours after fohexol injection. Results: Mean GFR was well preserved in all four age-classes. The GFR range was 18-83 mL/min and declined with age. The Cockcroft-Gault prediction equation systematically underestimated measured GFR. A new 'GFR(A)' prediction equation is presented, based on the inverse of serum cystatin C and independent of gender, body surface area, body weight, lean body mass or serum creatinine. The proposed equation underestimated measured GFR with a mean of only 0.1 mL/min, had better precision compared with the Cockcroft-Gault equation, and was evaluated by the method of cross-validation. Conclusions: GFR exhibits extensive heterogeneity in frail, community-dwelling elderly people. The proposed GFRA Was clearly more precise than the Cockcroft-Gault prediction equation in the study group. However, it needs to be validated in a larger population of elderly subjects, including more individuals in stable health with substantially reduced renal function in whom GFR is measured by a reference method with adequate sampling time.