Glomerular filtration rate with Tc99m DTPA. Comparison of methods

UNLABELLED: Glomerular filtration rate (GFR) is an important index of renal function. The aim of this study was to compare the GFR with 99m Tc. DTPA without urine collection estimated with three, two and single-sample methods. We studied 148 patients (54 women and 94 men, 3-84 years old) with diverse renal diseases. After intravenous administration of Tc99m DTPA three (90-120-180 min. Method 1; n = 44) or two (120 and 180 min or 180 and 240 min Method 2, n = 104) blood samples were taken. The GFR (ml/min) were calculated using monoexponential analysis, or with only the sample of the 180 or 240 min with the methods of Jacobsson, Russel, Groth-Aasted, Dakubu and Constable. RESULTS: 1) In 37/148 (25%) the GFR by Method 1-2 was less than 30 ml/min. All the single-sample methods did not perform well. 2) in 107/148 (75%) the GFR using method 1 and 2 was superior to 30 ml/min. The single sample methods showed clinically acceptable absolute error differences with method 1 and 2. However, we cannot suggest a preferable one single sample method that covers all the range of GFR that we analyzed. In conclusion, the 2 sample technique provides an estimate of GFR and we also suggest ultrafiltering the plasma before measuring radioactivity to give better accuracy in calculating GFR.