A comparison between estimates of GFR using [99m– Tc]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 ^99mTc]DTPA clearance, an accepted measure of GFR, is therefore of interest. Aim: To test prospectively the reliability of the formula in predicting the ^99mTc]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 ^99mTc]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 ^99mTc]DTPA clearance studied (14 to 125 mL/minute), in non-obese subjects, both Ccr and C_der were correlated similarly with ^99mTc]DTPA clearance in males and females. In obese subjects as a group, C_der was also closely correlated with ^99mTc]DTPA clearance but the scatter of data was wider. Among non-obese subjects, correlations were high between either Ccr or C_der and ^99mTc]DTPA clearance values < 101 mL/minute but were not significant at ^99mTc]DTPA clearance values > 100 mL/minute. For ^99mTc]DTPA clearance values between 14 and 100 mL/minute, C_der was a more direct and more precise predictor of ^99mTc]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_derC)- 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. (Aust NZ J Med 1993; 23: 494–497.)