The Detection of Deep Venous Thrombosis Using Labelled Urokinase

Abstract

The use of 125I-labelled fibrinogen in the detection of venous thrombosis in the lower limbs is well established. However, the technique is limited in applicability since only actively forming thrombi may be detected efficiently.Urokinase, a fibrinolytic enzyme, has been labelled with 99mTc and found to be suitable for the detection and localisation of venous thrombi. Iodinated urokinase has also been investigated. The use of 99mTc-labelled urokinase allows the lower limbs and the pelvis to be scanned using either a rectilinear scanner or a gamma camera, whereas with iodinated urokinase thohand monitor method used in the fibrinogen technique is used. The fibrinolytic activity of the labelled urokinase was evaluated using the fibrin plate technique in order to verify that the urokinase was not denatured in the labelling process. In the series of patients studied, venography was undertaken when possible for comparison with the urokinase scan.The time between the onset of clinical symptoms and urokinase scanning ranged from two days to several months suggesting that both active and formed thrombi may be detected. In order to exclude non-specific uptake by the thrombi, several patients with unilateral calf thrombosis were scanned with 99mTc-labelled human serum albumen.The labelled urokinase was injected intravenously and scanning initiated after 15 minutes in order to allow the circulating blood level to stabilise.