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PT (Prothrombin Time)

Prothrombin is a protein produced in the liver. It plays an important role in blood clotting: Reductions in prothrombin will lead to decreased clotting ability of the blood.

The PT (ProTime, Prothrombin Time) measures impairment of the clotting effects of prothrombin, fibrinogen, and coagulation Factors II, VII, IX, and X.

Any process that interferes with the production of prothrombin (liver disease, Vitamin K deficiency, Coumarin-based anticoagulants) may impair the ability of blood to clot, and can be measured by a prolongation of the Prothrombin Time (PT).

Patients being treated with oral anticoagulants are monitored with PT, to make sure they are within the therapeutic range.

  • If they aren't receiving enough anticoagulant, the treatment may be ineffective
  • If they receive too much anticoagulant, they may lose too much ability to clot and sustain injury as a consequence.

Prolonged PT is associated with:

  • Liver disease
  • Vitamin K deficiency
  • Anticoagulant (Coumarin, Coumadin) therapy
  • DIC

Therapeutic Range

  • 2-2.5 times the normal
  • Not more than 30 seconds

Normal Values*

Men-Women 10-14 seconds (100%)
Therapeutic Range on oral anticoagulants 2-2.5 times normal, but not >30 seconds

*These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.