Plasminogen Activator Inhibitor 1

Plasminogen activator inhibitor-1 (PAI-1) testing is indicated for unexplained mild-to-moderate delayed bleeding disorders, typically associated with trauma or surgery. ^[1]

Normal findings ^[2] :

• Antigen assay: 2-46 ng/mL
• Activity: < 31.1 IU/mL 

Increased PAI-1 activity is observed in acute-phase reactions associated with the following: ^[3]

• Inflammation

• Cancer

• Obesity

• Postoperative period

• Diabetes

• Atherosclerosis and atherothrombosis

• Pregnancy

Two types of inherited PAI-1 deficiency exist, as follows: ^[1]

• Type I: Decreased functional and immunological PAI-1 levels

• Type II: Decreased functional activity despite normal protein concentration

Specimen: Citrated plasma

Collection: Blue-top tube with 3.2% sodium citrate

Centrifugation: 2000-2500 g for 15 minutes or similar method to produce platelet-poor plasma

Storage: Up to 2 hours at 2-8°C or the plasma sample should be frozen; specimen is stable for one month at -20°C or 6-9 months at -80°C

A high concentration of bilirubin might affect the PAI-1 measurement. Lipemic or hemolyzed samples should not be used.

Antifibrinolytic drugs (aminocaproic acid, tranexamic acid) could interfere with assay results and should not be used.

Description

Plasminogen activator inhibitor-1 (PAI-1) is a glycoprotein (molecular weight, 47 kDa) that is synthesized in endothelial cells, hepatocytes, and adipocytes. It can also be released from activated platelets. PAI-1 circulates in the blood in both its active form (half-life of 30 minutes) and its latent form (half-life of 2 hours). PAI-1 is the main regulator of fibrinolytic system activation; it inhibits tissue-type plasminogen activators (tPA) and urokinase-type plasminogen activators (uPA). ^{[1, 3]}

Indications/Applications

PAI-1 testing is indicated for unexplained mild-to-moderate delayed bleeding disorders, typically associated with trauma or surgery. ^[1]

It is also indicated for idiopathic arterial or venous thromboembolism if other causes of thrombophilia are excluded. ^[4]

Considerations

The PAI-1 level has a diurnal variation, peaking in the early morning. ^[3] Repeated measurements of PAI-1 level or antigen or other fibrinolytic markers might be useful in confirming a persistently abnormal PAI-1 level as a cause of bleeding or thrombosis. ^{[1, 3]}