Accuracy of 2- and 8-hour urine collections for measuring creatinine clearance in the hospitalized elderly.

The accuracy of 2- and 8- hour urine collections for estimating creatinine clearance was compared with that of the standard 24-hour procedure in 45 hospitalized elderly patients (age > or = 65 yrs) with indwelling urethral catheters. Urine was collected at blocked intervals from 0-2, 2-8, and 8-24 hours and then added together to determine the 8- and 24-hour clearances. The mean 8-hour creatinine clearance was not significantly different from the 24-hour value, whereas the mean 2-hour creatinine clearance was significantly different. The 8-hour value was less biased (2.2 and 10.7 ml/min, respectively) and more precise (11.7 and 25.3 ml/min, respectively) than the 2-hour value. Regardless of age, renal function, serum creatinine level, or diuretic use, the 8-hour value was less biased, usually more precise, and clinically more accurate. Thus it can be used in stable, hospitalized, elderly patients with indwelling catheters to determine degrees of renal impairment and provide optimum drug dosing.