Measured versus estimated creatinine clearance in the elderly as an index of renal function.

Measured endogenous creatinine clearance (requiring 24-hour urine collection) was compared to estimated (calculated) creatinine clearance obtained by 2 formulas and a nomogram (without urine collection), in 26 elderly nursing home residents. All were clinically stable and had adequate intakes of food and fluid. Of the 26 subjects, 23 had a "normal" value for serum creatinine concentration (0.7-1.5 mg/dl) with a mean of 1.1 mg/dl. Measured creatinine clearance (Cer) was reduced in all patients despite a "normal" serum creatinine level. The mean Cer was 47.2 ml/min, with values as low as 21.6 ml/min. Measured Cer findings compared well with estimated (calculated) findings, the correlation coefficients being highly significant in all instances. If it is difficult or impossible to collect a 24-hour urine specimen, a fairly accurate assessment of renal function may be obtained by using a simple formula (or nomogram) for estimating creatinine clearance on the basis of the patient's age, weight (height) and serum creatinine level.