Type of test Blood
Normal findings
Antigen assay: 2-46 ng/mL
Activity: < 31.1 IU/mL
Test explanation and related physiology
PAI-1 is a protein that inhibits plasminogen activators. During fibrinolysis, tissue plasminogen activator (tPA) converts plasminogen into plasmin. Plasmin plays a critical role in fibrinolysis by degrading fibrin ( Figure 1). PAI-1 is the primary inhibitor of tPA and urokinase plasminogen activator (uPA) in the blood. PAI-1 limits the production of plasmin and keeps fibrinolysis in check.
Fig1. Secondary hemostasis (fibrin clot formation) and fibrinolysis (fibrin clot dissolution). Primary hemostasis involves platelet plugging of the injured blood vessel. Secondary hemostasis, as described here, takes place most rapidly on the platelet surface after attachment to the fractured endothelium. Four different reactions result in the formation of fibrin. As seen beneath the dark line in the figure, the fibrin clot supports the platelet clump so that the clot does not get swept away by the tremendous shear forces of the fast moving blood cells. Fibrinolysis follows formation of the fibrin clot in order to prevent complete occlusion of the injured blood vessel.
Elevated levels of PAI-1 are associated with a predisposition to thrombosis, including veno-occlusive disease after bone marrow transplantation or high-dose chemotherapy. Familial throm bosis has been associated with inherited elevation of plasma PAI-1 activity. Increased levels of PAI-1 have also been reported in a number of conditions, including malignancy, liver disease, the postoperative period, septic shock, the second and third trimesters of pregnancy, obesity, coronary heart disease, and restenosis after coronary angioplasty. Increased levels may reduce the effectiveness of antithrombolytic therapy. Patients with insulin resistance syndrome and diabetes mellitus tend to have increased PAI-1 levels.
Low plasma levels of the active form of PAI-1 have been associated with abnormal, clinically significant bleeding. Complete deficiency of PAI-1, either congenital or acquired, is associated with bleeding manifestations that include hemarthroses, hematomas, menorrhagia, easy bruising, and postoperative hemorrhage.
Interfering factors
• Because PAI-1 is an acute-phase reactant, it can become transiently elevated by infection, inflammation, or trauma.
• Levels increase during pregnancy.
• PAI-1 has a circadian rhythm, with the highest concentrations occurring in the morning and the lowest concentrations in the afternoon and evening.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: light blue
• Discard the first several milliliters of blood if PAI-1 is the only test being drawn. If multiple tests are being drawn, fill the light blue–top tube after any red-top tube.
• Gently invert the blood tube several times after collection.
Abnormal findings
Increased levels
-Acute coronary syndrome
- Coronary artery disease
- Restenosis after coronary angioplasty
- Infection
- Inflammation
- Trauma
- Diabetes mellitus
- Insulin resistance syndrome
- Pregnancy
Decreased levels
- Bleeding disorders
