The role of the fibrinolytic system in deep vein thrombosis.

Some aspects of the function of the fibrinolytic system have been investigated in 37 patients with a recent incident of symptomatic and confirmed deep vein thrombosis and compared with findings in 20 healthy persons. New specific methods to measure tissue plasminogen activator (t-PA) activity and antigen before and after venous occlusion and the recently discovered fast inhibitor to t-PA were employed. Thirteen of the patients with deep vein thrombosis (35%) had t-PA activity less than 0.5 IU/ml after venous occlusion, whereas the lowest activity found among the healthy individuals was 0.56 IU/ml. The t-PA inhibitor level in the total patient group was 3.8 +/- 3.7 U/ml (range 0 to 15.0 U/ml; median 2.9 U/ml) as compared with 0.7 +/- 0.7 U/ml in the healthy (median 0.5, range 0 to 2.4 U/ml). In the 13 patients with low t-PA activity in postocclusion plasma samples the inhibitor level was 6.0 +/- 4.4 U/ml. Furthermore, in this group of patients a significantly lesser release of t-PA antigen (3.7 +/- 2.8 micrograms/L) was found as compared with that in the healthy individuals (9.5 +/- 6.0 micrograms/L). Thus, two months after their first incident of symptomatic deep vein thrombosis many of the patients (35%) were found to have decreased fibrinolytic activity. This is the result of highly increased plasma levels of a novel fast inhibitor toward t-PA in combination with a poor ability to release t-PA. Possibly the decreased fibrinolytic activity did play a role in the pathogenesis of deep vein thrombosis in these patients.