ESTIMATION OF GLOMERULAR-FILTRATION RATE USING CHROMIUM-51 ETHYLENE DIAMINE TETRAACETIC ACID AND TC-99M DIETHYLENE TRIAMINE PENTA-ACETIC ACID

Simultaneous measurements of the clearance rate of chromium-51 ethylen e diamine tetra-acetic acid (Cr-51-EDTA) and technetium-99m diethylene triamine penta-acetic acid (Tc-99m-DTPA) were performed in 54 patient s with a range of function between 9 and 176 ml/min. Using multiple bl ood samples the two clearance values correlated well (r = 0.97, SEE 8. 6 ml/min) and DTPA clearance was higher by 2.9%. For each radiopharmac eutical the plasma clearance rates obtained using multiple blood sampl es were compared with those obtained with simplified methods, i.e., th e 60-180 min two-sample method of Russell and the mono-exponential met hod with the Brochner-Mortensen correction. For both radiopharmaceutic als the clearance values correlated well with the Russell method (r = 0.99, SEE = 4.1 ml/min for EDTA; r = 0.99, SEE 4.9 ml/min for DTPA) an d the mono-exponential method (r = 0.99, SEE 3.6 ml/min for EDTA; r = 0.99, SEE 3.9 ml/min for DTPA). The mean plasma clearance obtained usi ng multiple blood samples did not differ significantly from that obtai ned with the Russell method, either in patients with a glomerular filt ration rate (GFR) < 30 ml/min or in patients with GFR greater than or equal to 30 ml/min. The mean plasma clearance obtained using multiple blood samples differed significantly from that obtained with the mono- exponential method because of the great difference observed in patient s with GFR greater than or equal to 30 ml/min. It is concluded that th e Russell two-sample method after injection of Tc-99m-DTPA is accurate enough for routine clinical use.