Glomerular filtration rate in children: determination from the Tc-99m-DTPA renogram

Analysis of the Tc-99m-DTPA renogram is usually limited to calculating the relative function of each kidney. To develop a method to determine the absolute glomerular filtration rate (GFR), various methods of analyzing the renogram were examined to determine which gave the best correlation with GFR. That regression could then be used to predict GFR without the need for blood samples. Fifty children were studied using Tc-99m-DTPA renograms and GFR measured simultaneously by plasma disappearance. The renogram variables were adjusted for detector sensitivity and for dose divided by weight, which was used as an index of plasma concentration. GFR correlated better with the slope of the second phase than with the area under the renogram curve. For the best correlation with GFR (using background subtraction and depth correction) r = .971 and the mean residual = 4.8 ml/min. For GFR normalized for body surface area (using background subtraction and no depth correction) r = .954 and the mean residual = 9.1 ml/min/1.73 m2. This method can accurately estimate GFR from the renogram in children.