Can creatinine clearance be accurately predicted by formulae in octogenarian in-patients?

Background: As serum creatinine is relatively inaccurate for estimating renal function, prediction formulae are commonly used for more precise renal function estimation. However, these equations have not been studied in acutely hospitalized octogenarian patients. Aim: To compare three commonly used formulae for estimating GFR to measured creatinine clearance (CCR) in patients aged greater than or equal to80 years admitted to an acute geriatric department. Design: Prospective, observational study. Methods: Consecutive patients aged greater than or equal to80 years with urinary catheters, admitted over a 12-month period to the acute geriatric ward of a 600-bed university hospital, were enrolled in the study. All had an accurate 24-h urinary collection, as well as serum and urinary urea and creatinine determinations. CCR was calculated and compared with GFRs derived from the three formulae. Results: Of the 154 patients enrolled in the study, 107 (69.5%) had normal serum creatinine (less than or equal to1.4 mg/dl), but 77/107 (50.0%) of these had measured CCR less than or equal to60 ml/min/1.73 m(2). Mean CCR was 45.1 ml/min/1.73 m(2) declining at the rate of 1.1 ml/min/1.73 m(2) each year. Only 9% of patients according to the Cockcroft and Jelliffe formulae, and 17% by the MDRD formula, fell within -10% and +10% of the measured CCR, which were the limits of agreement decided prior to the initiation of the study. Discussion: Many elderly in-patients with moderate renal dysfunction will remain misidentified by relying on serum creatinine or commonly used prediction equations. The best practical approach in these patients is to avoid potentially nephrotoxic drugs and drugs excreted mainly through the kidneys.