Obesity, hyperfiltration and early kidney damage: a new formula for the estimation of creatinine clearance

Objective: Glomerular hyperfiltration may represent a direct pathogenetic link between obesity and kidney disease. The most widely used methods to estimate creatine clearance such as Cockroft-Gault (CG), Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) have not been validated in subjects with obesity. The performance of prediction formulas was compared to measured creatinine clearance (mCrCl) in subjects with obesity. Methods: The study population included 342 patients with obesity (mean BMI 47.6 kg/m2) without primary kidney disease. A urine collection was performed over 24 hours for measurement of CrCl. Results: mCrCl increased with body weight. The CG formula showed an overestimation at high CrCl, whereas an underestimation resulted from CKD-EPI and MDRD. To improve the accuracy of estimated CrCl (eCrCl), a new CG-based formula was developed as follow: 53+0.7 × (140-Age) × Weight/(96xSCr) × (0.85 if female)A cut-off point for BMI of 32 Kg/m2 was identified, at which the new formula may be applied to improve eCrCl. Conclusions: In patients with obesity the glomerular filtration rate increases with body weight, and it is associated with the presence of albuminuria, suggesting an early kidney injury. We propose a novel formula that improves the accuracy of eCrCl to avoid missed diagnoses of hyperfiltration in patients with obesity.