A COMPARISON BETWEEN ESTIMATES OF GFR USING [TC-99M] DTPA CLEARANCE AND THE APPROXIMATION OF COCKCROFT AND GAULT

Background. The formula of Cockcroft and Gault, relating age, weight, sex and plasma creatinine is widely used to estimate glomerular function. Its ability to predict [Tc-99m]DTPA clearance, an accepted measure of GFR, is therefore of interest. Aim: To test prospectively the reliability of the formula in predicting the [Tc-99m]DTPA clearance in subjects with normal and sub-normal renal function. Methods: The 24 hour creatinine clearance (Ccr), the derived clearance using the formula (C(der)), and the [Tc-99m]DTPA clearance have been compared in 47 male and 47 female subjects, aged between 15 and 71 years. Obese and non-obese subjects (males > 90 kg, females > 80 kg body weight) were considered separately. Results. Across the range of [Tc-99m]DTPA clearance studied (14 to 125 Ml/minute), in non-obese subjects, both Ccr and C(der) were correlated similarly with [Tc-99m]DTPA clearance in males and females. In obese subjects as a group, C(der) was also closely correlated with [Tc-99m]DTPA clearance but the scatter of data was wider. Among non-obese subjects, correlations were high between either Ccr or C(der) and [Tc-99m]DTPA clearance values < 101 mL/minute but were not significant at [Tc-99m]DTPA clearance values > 100 mL/minute. For [Tc-99m]DTPA clearance values between 14 and 100 mL/minute, C(der) was a more direct and more precise predictor of [Tc-99m]DTPA clearance [DTPA clearance = 1.01(C(der)) + 2.34, with 95% confidence limits of +/- 18 mL/minute] than of Ccr [Ccr = 1.34(C(der)C) - 10.86, confidence limits +/- 28 mL/minute]. Conclusion: For very mild through to moderate renal failure, the formula of Cockcroft and Gault can evidently be used as a reasonable estimate of GFR.