Estimation of glomerular filtration rate using chromium-51 ethylene diamine tetra-acetic acid and technetium-99m diethylene triamine penta-acetic acid.

Simultaneous measurements of the clearance rate of chromium-51 ethylene diamine tetra-acetic acid (51Cr-EDTA) and technetium-99m diethylene triamine penta-acetic acid (99mTc-DTPA) were performed in 54 patients with a range of function between 9 and 176 ml/min. Using multiple blood 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 radiopharmaceutical the plasma clearance rates obtained using multiple blood samples were compared with those obtained with simplified methods, i.e., the 60-180 min two-sample method of Russell and the mono-exponential method with the Brochner-Mortensen correction. For both radiopharmaceuticals 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) and 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 using multiple blood samples did not differ significantly from that obtained with the Russell method, either in patients with a glomerular filtration rate (GFR) < 30 ml/min or in patients with GFR > or = 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 patients with GFR > or = 30 ml/min. It is concluded that the Russell two-sample method after injection of 99mTc-DTPA is accurate enough for routine clinical use.