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.

Predictive performance of equations to estimate creatinine clearance in hospitalized elderly patients.

OBJECTIVE: To ascertain the clinical accuracy of equations that estimate creatinine clearance to predict the correct drug doses in hospitalized elderly patients DESIGN: Single 24-hour creatinine clearance measurement compared with estimated creatinine clearances derived from eight equations using total and modified ideal body weight SETTING: Nonintensive care medical and surgical units at a county hospital PATIENTS: 15 patients with urethral catheters were enrolled in each of three age groups: 65-75, 76-85, and greater than or equal to 86 years MAIN OUTCOME MEASUREMENTS: Drug-dose predictions, bias, precision, and absolute errors RESULTS: The bias for all equations was -4.0-42.0 mL/min (-0.07-0.70 mL/s) and the precision was 10.8-47.4 mL/min (0.18-0.88 mL/s). The Jelliffe 1973, Hull et al., and Mawer et al. equations were the least biased and the Jelliffe 1973 was the most precise, followed by the Mawer et al., Hull et al., and Cockcroft-Gault equations. The percent of patients with absolute percent errors greater than 20 percent were 38 percent for Jelliffe 1973, 36 percent for Mawer et al., 40 percent for Hull et al., and greater than 50 percent for the other equations. The percent of patients receiving correct drug doses was 67 percent for Jelliffe 1973, 58 percent for Gates, 51 percent for Mawer et al. and Hull et al., and less than 50 percent for the other equations. Within various age, renal function, serum creatinine, and albumin subgroups, the Jelliffe 1973 estimates were least biased and most precise, followed by the Cockcroft-Gault estimates. Generally, estimates using modified lean body weight performed better than did those using total body weight. CONCLUSIONS: The Jelliffe 1973 equation with modified lean body weight was the best equation, followed by the Cockcroft-Gault equation. Even with the best equation, 33 percent of the patients would have received an incorrect drug dose. Therefore, some elderly patients may still require a measured creatinine clearance.