Correlation of Methods of Glomerular Filtration Rate Estimation - 24 h Urinary Creatinine Clearance, Predicted Creatinine Clearance Method (Cockcroft-Gault), and Camera Based TC-99m- diethylenetriaminepentaacetic Acid Renography in Patients of Diabetic Nephropathy

Introduction: Glomerular filtration rate (GFR) is the most important measure for early detection of deterioration of renal function. Patients with diabetic nephropathy need to be intensely monitored with GFR value. Many methods are used to estimate the GFR, all having their own advantages and constraints. The correlation of these methods with each other in patients with diabetic nephropathy needs to be studied. Purpose: To correlate three widely used methods of GFR estimation, namely 24 h urinary creatinine clearance (CrCl), predicted CrCl method (Cockcroft-Gault [CG]), and camera based Tc-99m-diethylenetriaminepentaacetic acid (DTPA) renography (by Gates’ protocol), in cases of diabetic nephropathy and to study the effect of duration of disease on renal function. Materials and Methods: A total of 52 cases of diabetic nephropathy were studied, and GFR was estimated by all the above three methods simultaneously. Correlation between variables was performed using commercially available statistical software (Minitab 15). Bland-Altman recommendations were used to compare the GFR calculated with CG formula and 24 h CrCl with the TC-99m-DTPA renogram method. Pearson’s correlation was used to assess the relationship between variables. Results: The mean GFR obtained with 99mTc-DTPA renogram, 24 h CrCl, and CG method were 63.24 ml/min ± 22.39 ml/min, 43.06 ± 13.83 ml/min, and 54.87 ± 18.25 ml/min, respectively. There was a significant correlation between GFR by 99mTc-DTPA versus endogenous CrCl (P < 0.001, r = 0.830) and 99mTc-DTPA versus CG formula (P < 0.001, r = 0.919). Conclusion: There is a wide variation in the absolute values of GFR obtained by the three methods although all the three methods correlate well with each other. If the same method is used for follow-up, it is highly reliable in detecting the deterioration of renal function from the baseline value. However, these methods cannot be used interchangeably.