Plasminogen activator inhibitor (PAI)

Last updated: Saturday, 20, March, 2004

This assay is rarely performed and only in specialised laboratories.

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Item Process

4.5 mL blood added to 0.5 mL citrate.

  1. Functional assay: PAI activity measured by urokinase inhibition.
  2. Immunoassay.
Reference Interval

Guide only.

Functional assay: 0-3.5 U/mL
Immunoassay: 4-43 ng/mL.


Rarely performed. Investigation of recurrent thrombotic episodes.


PAI is an inhibitor of the fibrinolytic system.

Elevated levels may be found in acute myocardial infarction, malignancy, pre-eclampsia, infectious disease, and following surgery (trauma).


Dacie JV and Lewis SM. Practical Haematology. 8th ed. Churchill Livingstone 1995.