Comparison of 125I-labelled fibrinogen uptake and venography in the detection of recent deep-vein thrombosis in the legs.

Both techniques were used to examine 72 legs, and agreed about the presence or absence of thrombus in 54 cases (72 per cent). In 41 legs both tests were positive and in 13 legs both tests were negative. In 16 legs the 125I fibrinogen test only was positive, and if the seven legs with clinical conditions known to increase fibrinogen uptake are excluded, there were nine legs (13 per cent) with an increased fibrinogen uptake in the calf and a normal venogram. In two legs the venogram only was positive, and in both cases there was evidence of clot retraction which suggested that the thrombus was more than a week old. The use of radio-opaque markers attached to the skin made it possible to compare the site of thrombosis detected by the two techniques and the results of this comparison indicate that the fibrinogen test underestimated the extent of femoral vein thrombosis in a significant proportion of cases. (p less than 0-001).