Comparison of serum creatinine-based estimating equations with gates protocol for predicting glomerular filtration rate in indian population

In clinical practice, serum creatinine-based predicting equations and Gates protocol based on gamma camera imaging of kidneys after injection of Tc99m-diethylenetriaminepentaacetic acid (DTPA) are commonly used to assess glomerular filtration rate (GFR). Comparison of these methods, especially the chronic kidney disease-epidemiology collaboration (CKD-EPI) equation with gold standard method of assessment of GFR by plasma clearance of Tc-99mDTPA is not well-studied in Indian population. We conducted this study to compare GFR estimation by gamma camera-based Gates protocol and serum creatinine-based predicting equations with GFR measured by plasma clearance of Tc-99mDTPA. One hundred and five patients (65 male and 40 female) underwent Tc-99m DTPA renal scan followed by withdrawal of venous blood samples at 2, 3, and 4 h as per predefined protocol. Gates method GFR (GFR(s)) was assessed using standard protocol. GFR by plasma sampling (GFR(p)) was calculated by slope-intercept method with provision for corrections. Estimated GFR was calculated by Cockroft-Gault formula, four variable modification of diet in renal disease (MDRD) equation, and CKD-EPI equation (GFR(CG,) GFR(MDRD), GFR(CKD-EPI), respectively). GFR measured by gold standard method (GFR(p)) was compared with that estimated by other methods by calculating correlation coefficient, bias, precision, and accuracy. GFR estimated by all three estimating equations correlated better than GFR(s) with GFR(p.) For estimating GFR(p), GFR(CKD-EPI) had highest correlation with GFR(p) with least bias and highest precision. Gamma camera-based Gates protocol was the least precise and least accurate method for estimating GFR(p). To conclude, all three estimating equations based on serum creatinine are superior to Tc-99m DTPA scintigraphy for estimating GFR; CKD-EPI equation being the most accurate and precise.