Development of formulae for accurate measurement of the glomerular filtration rate by renal dynamic imaging

AIMCurrently, the widely adopted renal dynamic imaging in clinical practice uses Gatesʼ method to calculate the glomerular filtration rate (GFR), but many researchers have proven that Gatesʼ method may result in bias. Thus, this article explores alternative improved formulae to calculate GFR by renal dynamic imaging. METHODSThree hundred and sixty-seven patients were selected and their GFR values were measured using renal dynamic imaging and the two-plasma method with Tc-diethylenetriaminepentaacetic acid (Tc-DTPA) as the imaging agent. With the two-plasma GFR as reference value, two equations were obtained from linear and non-linear regression analyses between the renal uptake percentage and two-plasma GFR. The 367 patients were divided into two random groups, with the first group used to derive the regression formulae and the second to verify the formulae. Finally, all patients were studied to derive the formulae to calculate GFR. The comparison of our formulae with the commonly used Gatesʼ formula was conducted by the Bland–Altman method. RESULTSThe linear and non-linear GFR formulae were as followsGFR (ml/min/1.73 m)=(631.633×renal uptake percentage−2.040)×1.73/BSA (BSA, body surface area) and GFR (ml/min/1.73 m)=(−1996.585×renal uptake percentage+1013.526×renal uptake percentage−12.739)×1.73/BSA, respectively. The biases of the GFR values calculated using the linear and non-linear formulae and Gatesʼ formula relative to the two-plasma GFR were −2.5±19.1 ml/min/1.73 m, −2.0±19.3 ml/min/1.73 m and 3.4±19.4 ml/min/1.73 m, respectively. CONCLUSIONSThe GFR values calculated using our new formulae correlate better with the reference GFR value than does GFR calculated by Gatesʼ formula, and the GFR values measured using the non-linear formula are more accurate than those obtained using the linear formula.