• Jorge Vega, Juan Pablo Huidobro E, and SepúlvedaRodrigo ARADepartamento de Nefrología, Escuela de Medicina, Facultad de Medicina, Universidad Católica de Chile, Santiago, Chile..
• Servicio de Medicina, Hospital Naval A. Nef, Viña del Mar, Chile.
• Rev Med Chil. 2024 Jul 1; 152 (7): 798807798-807.

UnlabelledGlomerular filtration rate estimates are usually indexed to a standard body surface area (BSA) of 1.73 m2. This allows comparing values of individuals of different sizes but has the potential of affecting individuals with extremes BSA.Aimevaluating the differences in GFR estimates with or without indexing for BSA in a large cohort of ambulatory patients grouped by different body mass index (BMI) and how indexing affects CKD classification.Methodsdemographic and anthropometric data of 390 patients evaluated with ambulatory 24-hour creatinine clearance were registered in an anonymous database. Patients were divided in 3 groups according to BMI (18-24.9; 25-29.9; >30 kg/m2). GFR was estimated using creatinine clearance (CrCl), CKD-EPI 2009 and 2021 equations, both indexed to a standardized BSA of 1.73 m2 and using the actual BSA of the patients. CKD classification was performed with and without indexing.Results224 of 390 patients were men (57.4%). 103 (26.4%) had normal BMI (group 1), 193 (49.5%) BMI of 25-29.9 (group 2) and 94 (24.1%) had BMI of 30 or more kg/m2 (group 3). Mean CrCl was 67.9 +/- 32.7 ml/min. Indexed to a BSA of 1.73 m2 CrCl was 64.8 +/- 30.5 ml/min (difference of -3.1 ml/min) (p< 0.001). The difference between real and indexed CrCl was +2.2 ml/min, -2.9 ml/min y -9.3 ml/min in groups 1, 2 and 3, respectively. Real CrCl was significantly higher in group 3 compared to group 1. Indexed ClCr was similar between the 3 groups. GFR estimation using equations was over 2 mL/min higher when removing indexation for standard BSA. Group 1 had higher indexed GFR estimates than groups 2 and 3. However, when removing indexing the 3 groups had similar GFR estimates. Classification of CKD was significantly affected by removing indexing, with almost 20% of the patients changing CKD stage. Diagnosis of GFR <60 mL/min was less frequent when removing indexing.ConclusionIndexing to standard BSA lowers GFR estimation in overweight and obese patients, leading to a higher prevalence of GFR < 60 mL/min and CKD diagnosis.

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