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Prothrombin time determines the efficiency of the extrinsic coagulation system, that is, dependent on specific coagulation factors occurring outside the blood vessels. These factors are produced in the liver. Thanks to the defined prothrombin time, the course of therapy with drugs that reduce blood clotting, e.g. coumarin derivatives, which inhibit the production of coagulation factors in the liver, can be monitored.

Prothrombin Time (PT)can be expressed in several ways.Prothrombin Factory can be expressed as the difference in seconds between the PT of the test person and the control plasma. PT can be expressed as a percentage of prothrombin activity calculated from a normal plasma dilution curve. The so-calledQuick Indexshows PT as a percentage of prothrombin time. The prothrombin time ratio expressed in seconds andINR- the international normalized ratio are also possible. The value of the PT index depends on the presence of fibrinogen II, V, VII, X in the blood.

Prothrombin time: preparation and course of the blood test

You should be on an empty stomach for blood collection in order to determine the prothrombin time - no less than 8 hours have elapsed since the last meal. Blood is drawn from a vein in the arm.

Norms of results in the prothrombin time test

Norm: 13-17 sec. or 0.9-1.3 INR (2-4 INR therapeutic range) or 80-120% (Quick pointer).

Prothrombin time higher than normal

Above normal result may appear in:

  • cases of congenital deficiencies of factors II, V, VII, X
  • chronic diseases of the liver parenchyma
  • during treatment with vitamin K antagonists
  • in vitamin K deficiencies
  • with oral anticoagulants and non-steroidal anti-inflammatory drugs
  • coumarin intoxication
  • DIC
  • with significant fibrinogen deficiency
  • dysfibrinogenemia
  • leukemia
  • uremia
  • Addison-Biermer disease

Prothrombin time is lower than normal

The prothrombin time is shortened:

  • in thrombosis
  • thrombophilia
  • in the perinatal period
  • in increased factor VII activity

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