Validity of Estimated Glomerular Filtration Rate Equation and Assessment of Bio-Impedance Analysis in Advanced Chronic Kidney Disease Patients

Introduction: This cross-sectional study was conducted to validate estimated glomerular filtration rate (eGFR) equation and assess body composition in chronic kidney disease (CKD) stage 5 non-dialysis (ND) participants. Methods: : A total of 111 samples of Thai CKD stage 5 ND participants with eGFR below 15 mL/min/1.73 m 2 , calculated by using the CKD Epidemiology Collaboration (CKD-EPI) equation, were enrolled into the study. The 99mTc-DTPA plasma clearance was used as the reference GFR. Body composition analysis was measured by bio-impedance analysis (BIA) to assess volume as well as body composition. Results: : The mean isotope for GFR was 17.39±6.83 mL/min/1.73m 2 . The mean bias values between isotope GFR and re-expressed MDRD equation, CKD-EPI equation, Thai equation, and cystatin C-based equation were 8.89±6.35, 9.47±6.13, 2.05±6.80, and 5.50±6.40 mL/min/1.73m 2 , respectively. The accuracy (root-mean-square error) values were 13.05, 13.68, 8.73, and 10.58 mL/min, respectively. Using BIA, the low muscle mass was 33.66%, excessive fat was 55.00 %, and the presence of edema was 48.5%. Participants with low muscle mass, excessive fat, and subclinical edema had higher bias of GFR measurement for all equations. The bias values for eGFR in participants with low muscle mass, excessive fat, and subclinical edema by re-expressed MDRD equation were 10.23, 9.61, 10.88 mL/min/1.73m 2 ; by CKD-EPI equation: 8.49, 10.25, 11.63 mL/min/1.73m 2 ; by the Thai eGFR equation: 3.16, 2.73, 4.77 mL/min/1.73m 2 ; and by the cystatin C-based equation: 6.32, 6.6, 7.99 mL/min/1.73m 2 , respectively. Conclusions: The Thai equation was the most accurate and precise method to determine the renal function of Thai CKD stage 5 ND participants who had a high prevalence of low muscle mass, excessive fat, and subclinical edema. The result suggested that ethnic-specific eGFR equation should be recommended in advanced CKD patients. Alteration of the body composition in advanced CKD patients is of concern because it can affect the performance of all of the eGFR equations.