Ion D Bucaloiu1, G Craig Wood2, Evan R Norfolk1, Christopher D Still3, James E Hartle1, Robert M Perkins41Department of Nephrology, Geisinger Medical Center, Danville, PA; 2Biostatistics and Research Data Core, Henry Hood Center for Health Research, Geisinger Medical Center, Danville, PA; 3Center for Nutrition and Weight Management, Geisinger Medical Center, Danville, PA; 4Department of Nephrology and Henry Hood Center for Health Research, Geisinger Medical Center, Danville, PA, USAPurpose: Precise estimation of creatinine clearance in obese individuals relies on the appropriate assessment of lean body weight (LBW). Anthropometric methods of predicting LBW have not been validated in morbidly obese populations.Patients and methods: Using an existing dataset of anthropometric data for a female cohort with morbid obesity who had undergone measured FFW with dual energy absorptiometry, we evaluated the performance of five previously reported estimating equations for the prediction of LBW. Linear regression was used to derive a new LBW prediction formula and was then compared with the other formulae.Results: Seventy females (mean [standard deviation] age, weight, and body mass index 43.0 [11.0] years, 128.1 [13.8] kg, and 48.3 [4.8] kg/m², respectively) were identified. LBW as estimated by the method of Garrow and Webster correlated well (r = 0.87) with measured mass while demonstrating the highest accuracy, best precision, and smallest bias (93%, 2.1 kg, and 2.9 kg, respectively; P < 0.0001 for all comparisons). The derived formula further improved bias, precision, and accuracy.Conclusion: Among females with morbid obesity, most previously reported estimating equations for LBW predicted FFW poorly. These findings have important clinical implications for the assessment of kidney function and for safe and effective drug dosing.Keywords: body composition, body weight, creatinine clearance, kidney function, lean body mass, obesity, pharmacokinetics