Summary
An impaired fibrinolytic activity after a venous occlusion test is the most common
abnormality associated with thomboembolic disease. To better characterize the causes
of abnormal responses we have measured different fibrinolytic parameters, before and
after 10 and 20 min of venous occlusion, in 77 patients with a history of idiopathic
deep vein thrombosis and/or pulmonary embolism and in 38 healthy volunteers.
The patients had a lower mean fibrinolytic response to venous occlusion than the controls
and higher antigen levels of tissue-type plasminogen activator (t-PA: Ag) and plasminogen
activator inhibitor type 1 (PAI-1:Ag). Before venous occlusion, PAI-1 levels were
at a molar excess over those of t-PA in all patients and controls. After 20 min of
venous occlusion, the release of t-PA from the vascular endothelium resulted in a
molar excess of t-PA over PAI-1 in the majority of controls (72%) but only in a minority
of patients (39%).
To identify patients with fibrinolytic abnormalities, reference intervals (RI) for
fibrinolytic activity, t-PA:Ag and PAI-1:Ag were established in healthy controls.
None of the patients had low levels of t-PA:Ag, but 17 (22%) had elevated PAI-1:Ag
levels before venous occlusion and 12 (16%) exhibited low fibrinolytic activity after
20 min of venous occlusion. Ten of these were among the 17 subjects with high PAI-1:
Ag levels before venous occlusion. Thus, the measurement of PAI-1:Ag levels before
venous occlusion (i.e. in samples taken without any stimulation) is a sensitive (83%)
and specific (89%) assay for the detection of patients with an impaired fibrinolytic
response to venous occlusion.
