Estimation of glomerular filtration rate with a formula including lean body mass

Background: Accurate measures of glomerular filtration rate (GFR), which provide a useful index of renal disease severity, are required to help decide when to start dialysis and to estimate correct drug dosage. Serum creatinine concentration is widely used as an index of renal function, but it is affected by factors other than GFR. In this study, we researched affect of demographic and anthropometric variables on GFR. We aimed to develop a GFR estimation formula including lean body mass (LBM).Material and Method: We studied 81 patients (mean age 43.4±17.2) with cronic kidney disease (mean GFR 38.2±28.2 ml/dk/1.73m2). Actual GFR was measured by the Tc-99m DTPA. LBM was measured by the bioelectrical impedance analysis. We used linear regression analyses to develop new formulas.Results: The independent predictor factors of GFR in linear regression analysis were found to be 1/serum creatinine (SCr) in non-obese group (BMI<30 kg/m2) and LBM/SCr with Fatmass/SCr in obese group (BMI>30kg/m2). Age, sex, weight, height, albumin, and 24 hour urine protein excretion were not significantly predicted the GFR (p>0.05). Two different formula were develop with linear regression analyses for obese [GFH= (1.255xYVK?0.825xVYK)/Cr + 2.1 (if patients is woman) or + 11.4 (if patients is man)] and non-obese group [GFR=74.7/Cr +1 (if patients is man) or -3.5 (if patients is woman)]. The R2 value of new formulas was 0.828 as compared with actual GFR were measured by Tc-99m DTPA (p<0.05). We found more accurate results with our new formulas in comparison with Cockcroft and Gault (C&G), C&G adjusted LBM (C&G-LBM), Modification of Diet in Renal Disease (MDRD) formula and creatinine clearance (CrCl).Conclusion: New prediction equation more accurately estimated actual GFR in our study group than other commonly used equations. Body composition in obese subjects has significant impact on GFR estimation. Traditional formulas of estimating GFR must be cautiously used in obese subjects.Key words: glomerular filtration rate, chronic kidney disease, creatinine, lean body mass