The influence of body size descriptors on the estimation of kidney function in normal weight, overweight, obese, and morbidly obese adults.

Background: Dosing adjustments for patients with impaired kidney function are often based on estimated creatinine clearance (eCrCl) because measuring kidney function is not always possible for dose adjustment. However, there is no consensus on the body size descriptor that should be used in the estimation equations.

Objective: To compare the use of alternative body size descriptors (ABSDs) on the performance of kidney function estimation equations compared with measured CrCl (mCrCl).

Methods: We combined 2

Data sources: a Food and Drug Administration clinical trial database that includes subjects with body mass index (BMI) less than 40 kg/m(2) and published data from those 40 kg/m(2) or more. The 3 parent equations (Cockcroft-Gault [CG], Modification of Diet in Renal Disease [MDRD], Chronic Kidney Disease-Epidemiology Collaboration [CKDEPI]), and 14 ABSD-modified equations were compared with mCrCl for accuracy, bias, agreement, goodness of fit (R(2)), and prediction error. These equations were also compared across mCrCl and BMI strata.

Results: Subjects (n = 590) were aged 19-80 years; 33.9% were female and BMI ranged from 17.2 to 95.6 kg/m(2). Compared with mCrCl, the use of total weight in the CG equation yielded low accuracy (12.5%) and significant bias (-107 mL/min) in the morbidly obese group. In contrast, the use of lean body weights (BMI ≥40 kg/m(2)) and total ± adjusted weights (BMI <40 kg/m(2)) with the CG equation yielded higher accuracy, greater than or equal to 60.7% across all BMI strata, and was unbiased. Transforming the MDRD or CKDEPI equations with body surface area improved accuracy only at mCrCl of 30-80 mL/min and increased the overall prediction error.

Conclusions: No kidney function equation was consistently accurate and unbiased across weight, mCrCl, and estimate ranges. The accuracy and overestimation bias of the CG equation in obese subjects was improved through the selective use of total, adjusted, and lean body weight by BMI strata.