Estimating creatinine clearance in morbidity obese patients.

Estimates of creatinine clearance (Clcr), using five methods, were compared to measured Clcr in morbidity obese patients. Patients whose total body weight (TBW) was greater than or equal to 195% of their ideal body weight (IBW) and who had urinary Clcr measured with 24-hour urine collections were studied. The 12 men weighed an average of 180 kg; the 31 women averaged 138 kg. The methods studied considered a combination of the following factors: weight, age, sex, and serum creatinine. One method was a nomogram; TBW could not be used because of limitations of the nomogram. Both TBW and IBW were used in two methods that considered weight as a variable. Measured Clcr averaged 105.7 ml/min/1.73 sq m body surface area. All estimating methods using IBW significantly underestimated Clcr; all methods using TBW significantly overestimated Clcr. Two methods that did not include body weight as a variable predicted Clcr more accurately than did other methods, but there was still a significant difference between estimated and measured Clcr. None of the Clcr estimation methods is accurate in morbidly obese patients.