The body composition and excretory burden of lean, obese, and severely obese individuals has implications for the assessment of chronic kidney disease.
Obesity could affect associations between creatinine generation, estimated body surface area, and excretory burden, with effects on chronic kidney disease assessment. We therefore examined the impact of obesity on the performances of estimated glomerular filtration rate (eGFR), the urine albumin:creatinine ratio (ACR), and excretory burden in 3611 participants of the Chronic Renal Insufficiency Cohort. Urine creatinine excretion significantly increased with body mass index (BMI) (34 and 31% greater at 40?kg/m(2) or more versus the normal of 18.5-25?kg/m(2)) in men and women, respectively, such that patients with a normal BMI and an ACR of 30?mg/g had the same 24-h albuminuria as severely obese patients with ACR 23?mg/g. The bias of eGFR (referenced to body surface area-indexed iothalamate (i-)GFR) had a U-shaped relationship to obesity in men but progressively increased in women. Nevertheless, obesity-associated body surface area increases were accompanied by a greater absolute (non-indexed) iGFR for a given eGFR, particularly in men. Two men with eGFRs of 45?ml/min per 1.73?m(2), height 1.76?m, and BMI 22 or 45?kg/m(2) had absolute iGFRs of 46 and 62?ml/min, respectively. The excretory burden, assessed as urine urea nitrogen and estimated dietary phosphorus, sodium, and potassium intakes, also increased in obesity. However, obese men had lower odds of anemia, hyperkalemia, and hyperphosphatemia. Thus, for a given ACR and eGFR, obese individuals have greater albuminuria, absolute GFR, and excretory burden. This has implications for chronic kidney disease management, screening, and research.Kidney International advance online publication, 9 April 2014; doi:10.1038/ki.2014.112.