Technetium-99m-modified recombinant tissue plasminogen activator to detect deep venous thrombosis

We report a method for deep venous thrombosis (DVT) detection which uses 99mTc-labeled modified recombinant tissue plasminogen activator (rt-PA) scintigraphy. A Phase III clinical trial was performed on 79 patients with suspected DVT.

The plasminogen binding site of rt-PA was permanently inhibited without inactivating the fibrin binding site. The modified molecule was radiolabeled with 99mTc. Scintigraphy was performed and the results were compared to those of contrast venography.

Of 14 thrombosed proximal segments, 13 had positive scans; in the 53 nonthrombosed proximal segments, 49 had negative scans. In proximal vein thrombosis, rt-PA scintigraphy had a sensitivity of 93% and a specificity of 92%. Of the 36 thrombosed calf vein segments, 31 had positive scans; in the 30 nonthrombosed calf segments, 28 had negative scans. In calf vein thrombosis, scanning has a sensitivity of 86% and a specificity of 93%.

Scintigraphic scanning with this 99mTc modified rt-PA permits accurate detection of thrombus in both proximal and calf veins in patients with clinically suspected DVT. The technique detects both fresh and aged thrombi and is unaffected by heparin administration. Further study in other patient groups is needed to define the overall clinical utility.