Kidney Week

Abstract: TH-PO1037

Indexing to Body Surface Area Diminishes GFR Estimation and Increases CKD Staging in Overweight and Obese Population

Session Information

• CKD Progression and Complications: Diagnosis, Prognosis, Risk Factors
  November 02, 2023 | Location: Exhibit Hall, Pennsylvania Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: CKD (Non-Dialysis)

• 2302 CKD (Non-Dialysis): Clinical, Outcomes, and Trials

Authors

• Huidobro, Juan Pablo, Pontificia Universidad Catolica de Chile, Santiago, Chile

Juan Pablo Huidobro,

• Sepúlveda, Rodrigo, Pontificia Universidad Catolica de Chile, Santiago, Chile

Rodrigo Sepúlveda,

• Vega, Jorge E., Universidad de Valparaiso, Valparaiso, Chile

Jorge E. Vega,

Background

Estimated glomerular filtration rate (eGFR) is usually indexed to a standard body surface area (BSA) of 1.73m². This allows comparing values of individuals of different sizes but can potentially affect eGFR in individuals with extreme BSA. We aimed to evaluate the differences in eGFR with and without indexing for BSA in a cohort of ambulatory patients with different body mass index (BMI) and how indexing affects CKD classification.

Methods

390 patients of a nephrological clinic were evaluated with ambulatory 24-hour creatinine clearance (CrCl) and their demographic and anthropometric data was 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 with MDRD-4, CKD-EPI 2009 and 2021 equations, with and without indexing to 1.73m². CKD classification was also performed with and without indexing eGFR.

Results

224 of 390 patients were men (57.4%).103 (26.4%) had normal BMI (group 1), 193 (49.5%) were overweight (group 2) and 94 (24.1%) were obese (group 3).
The difference between non-indexed and indexed CrCl was +2.2 ml/min, - 2.9 ml/min y – 9.3 ml/min in groups 1, 2 and 3, respectively. Using MDRD-4, CKD-EPI 2009 and 2021 equations, the differences were -2.0, -2,1 and -2,2 in group 1; +2.2, +2,3 and +2,5 in group 2; and +7.3, 7,6 and +8.0 ml/min in group 3. Non-indexed eGFR was significantly higher in obese patients (p<0.001).
Classification of CKD was significantly affected by removing indexing using CKD-EPI 2021 equation, with almost 20% of the patients switching stage of CKD (17.5% group 1, 18.7% group 2 and 12.8% group 3). Diagnosis of GFR <60 mL/min was more frequent when GFR estimation was indexed in overweight and obese patients (15% and 13.3% more, respectively). Converserly, removing indexing reclassifies 11.7% of patients with normal BMI into GFR <60 mL/min.

Conclusion

Indexing to standard BSA lowers eGFR in overweight and obese patients, leading to a higher prevalence of < 60 ml/min CKD diagnosis.