Venous Occlusion Test
The venous occlusion test is an approach for studying fibrinolysis. Impaired fibrinolysis, determined by low fibrinolytic activity [e.g. increased ECLT] following venous occlusion has been reported to be associated with a variety of clinical problems including spontaneous or recurrent
deep vein thromboses.
Deficient Fibrinolysis may be due to:
- ↑Plasminogen activator inhibitor (PAI) levels
- ↓Release of tissue plasminogen activator (t-PA) from the vascular endothelium
- A functionally abnormal t-PA
Historically the venous occlusion test was a commonly performed test but it rarely performed today. The test relies upon the observation that following a period of venous occlusion there is an increase in the fibrinolytic activity of plasma, The mechanisms underlying the fibrinolytic response are poorly understood - it is possible that venous occlusion stimulates t-PA release but alternatively it may be due to an accumulation of t-PA that it continually secreted by endothelial cells.
Principles & Method
The test involves placing a BP cuff around the arm and inflating it to mid-way between the systolic and diastolic blood pressures [but <100mm Hg] for a period of 10-20 minutes. Blood samples are collected before and after the venous occlusion [distal to the cuff with the cuff still inflated] and the fibrinolytic activity of the plasma established.
Interpretation & Reference Ranges
The interpretation of the results is difficult:
1. In healthy individuals, a shortening of the ECLT will be observed and in general this is reduced by at least 30 minutes.
2. In most healthy individuals there will be increase in t-PA:Ag and t-PA activity and a decrease in PAI-1 antigen and PA-1 activity.
3. 'Poor responders' are commonly defined as those who after venous occlusion defined as patients who, after venous occlusion shows defective release of t-PA activity or t-PA:Ag (calculated as below the lowest value measured in a control population.
What Test Next
Individuals with defective fibrinolysis measured by venous occlusion and global tests of fibrinolytic activity e.g. ECLT and fibrin plate lysis , may go on to have specific assays of t-PA and PAI-1 [or plasminogen] measured.
Click HERE to go to the Data Interpretation Exercises.