A comparison between estimates of GFR using [99m– Tc]DTPA clearance and the approximation of Cockcroft and Gault

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Abstract
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. To test prospectively the reliability of the formula in predicting the [99mTc]DTPA clearance in subjects with normal and sub-normal renal function. The 24 hour creatinine clearance (Ccr), the derived clearance using the formula (Cder), and the [99mTc]TPA 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. Across the range of [99mTc]DTPA clearance studied (14 to 125 mL/minute), in non-obese subjects, both Ccr and Cder were correlated similarly with [99mTc]DTPA clearance in males and females. In obese subjects as a group, Cder 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 Cder 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, Cder was a more direct and more precise predictor of [99mTc]DTPA clearance [DTPA clearance = 1.01 (Cder) + 2.34, with 95% confidence limits of +/- 18 mL/minute] than of Ccr [Ccr = 1.34(CderC)-10.86, confidence limits +/- 28 mL/minute]. For very mild through to moderate renal failure, the formula of Cockcroft and Gault can evidently be used as a reasonable estimate of GFR.