Glomerular Filtration Rate Prediction Formulas in Obese Persons with Chronic Renal Impairment

Overview

Background.
The glomerular filtration rate (GFR) could be estimated on the basis of serum creatinine concentration (S_cr) and some simple variables and demographic data. In clinical practice the most used methods for GFR estimation are Cockcroft – Gault (CG) formula and abbreviated MDRD equation (MDRD abr). The aim of this study was to evaluate how far obesity could affect GFR estimation based on the above formulas. 

Methods and Results.
In 291 patients with chronic renal impairment (S_cr 45–489 μmol/l) GFR was examined on the basis of renal inulin clearance (C_in) and estimated using MDRD abr and CG (without correction for body surface area-BSA and CG corrected for BSA) (CG_korig). The group of nonobese patients (A) consisted of 229 patients (BMI <30 kg/m²) and the group of obese patients (B) consisted of 62 patients (BMI 30 kg/m²). The values of r (r²) for MDRD abr, CG and CG_korig in group A of patients was as follows: 0.893 (0.797), 0.810 (0.651), 0.853 (0.727) and 0.853 (0.727). In obese patients (group B) the corresponding values were as follows: 68.3 % (82.6 %), 28.6 % (39.7 %) and 46 % (61.9 %). Predicted GFR within 30 % and 50 % of C_in (in brackets), CG and CG_korig (for BSA) were for group A: 70.2 % (87.3 %), 50.4 % (67.1 %) and 55.7 % (75 %) and for group B: 68.3 % (82.6 %), 28.6 % (39.7 %) and 46 % (61.9 %). The ratio MDRD abr/C_in did not correlate with BMI. A weak, but significant correlation was found between BMI and CC_korig/C_in ratio (r=0.22, p<0.05).  

Conclusions.
The obtained results suggest that estimation of GFR based on MDRD abr is not influenced by obesity. Estimation of GFR based on CG formula is significantly affected by obesity. A weak but significant relation could by found between CG_korig/C_in and BMI. 

Key words:
prediction glomerular filtration rate, MDRD, obesity.