ACCURACY OF ESTIMATED CREATININE CLEARANCE IN OBESE PATIENTS WITH STABLE RENAL-FUNCTION IN THE INTENSIVE-CARE-UNIT

We compared agreement between creatinine clearance values in obese, cr itically ill patients calculated using three common empirically derive d formulas and modifications thereof, with creatinine clearance obtain ed by conventional 24-hour urine collection. We selected the charts of of 22 patients in intensive care units (86% medical, 14% surgical) ac cording to the following criteria: actual body weight greater than 150 % of ideal body weight; serum creatinine variation of less than 15% fr om the day of starting 24-hour urine collection to the day before or a fter the collection; presence of a urinary bladder catheter; no histor y of renal dialysis; and clinical indication for renal function assess ment. Mean measured 24-hour urinary creatinine clearance for all patie nts was 72 +/- 64 ml/minute (range 8-248 ml/min). The method of estima ting creatinine clearance that showed the least mean bias was the equa tion of Salazar and Corcoran using a corrected serum creatinine concen tration (mean bias -2 ml/min); however, the corresponding 95% confiden ce intervals were wide (-133-129 ml/min). The narrowest range of 95% c onfidence intervals were seen with Jelliffe's equation (mean bias 25 m l/min, 95% confidence intervals -41-90 ml/min). In this sample, estima ted creatinine clearances did not agree acceptably with measured value s. Despite low mean bias values, none of the empirically derived equat ions that we studied had clinically acceptable 95% confidence interval s. We recommend using the 24-hour urine collection method when assessi ng creatinine clearance in obese, critically ill patients.