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Prothrombin time, index, international normalized ratio

Known as: prothrombin
SKU: 1100


Study material: Venous blood
Response time (working day): 1
The test is done on an empty stomach: Yes
Home call service: Yes
Country: Georgia

General Information

Prothrombin Is a protein synthesized by the liver and is one of the important factors that promotes blood clotting. Normal coagulation requires several types of proteins called coagulation factors. In the process of coagulation they must act properly and in sufficient quantities.


When should we take the test?

  • Evaluation of the activity of vitamin K-dependent coagulation factors.
  • Suspected congenital deficiency of coagulation factors (hereditary hemophilia and II, V, VII, X and fibrinogen factors).
  • Monitoring treatment with anticoagulants (syndrome, etc.).
  • Monitor liver function (assess its protein-producing function) and detect its abnormalities.
  • Eliminate blood clotting disorders before surgery or invasive procedures.
  • Suspicion of DIC syndrome (disseminated intravascular coagulation syndrome).
  • Suspicion of dysphibrinogenemia.
  • Suspicion of vitamin K deficiency.
  • When prone to bleeding (prolonged bleeding, frequent bleeding, bleeding from the nose and gums, spontaneous ecchymoses)
  • Venous thrombosis.
  • Recommended for Sars-cov2 infection to monitor thrombosis prevention.

It is advisable to perform the above tests:

  • For annual prophylactic examinations. The frequency of coagulation test for prophylaxis depends on the age of the patient: for young people it is recommended once a year, for the elderly - once every 6 months.
  • See also When infected with SARS-CoV-2, To prevent thrombosis.

The examination is prescribed by a doctor.

Possible interpretation of the results

Prothrombin time is usually measured in seconds, but can also be expressed in other ways:

  • Measured In seconds: The norm in healthy patients - 10-14 seconds
  • Measured In percentages: Normal prothrombin activity - > 70%.
  • Measured By INR: The norm in healthy patients - INR 0.8 - 1.2.
  • Therapeutic interval in patients receiving oral anticoagulant therapy: INR 2,0 - 3,0.


Prolongation of prothrombin time Means inhibition of blood clotting and is manifested in the following cases:

  • Anticoagulant therapy.
  • Impaired liver function.
  • Insufficient amount of blood clotting proteins.
  • Vitamin K deficiency.
  • Deficiency of other coagulation factors (f. II, V, VII or X).
  • DIC syndrome.
  • Presence of blood clotting inhibitors.

Reduced prothrombin time Means accelerated blood clotting and has no clinical significance. Manifested in the following cases:

  • Take vitamin K supplements.
  • Take large amounts of vitamin K products (green tea, liver, broccoli, soy).
  • Estrogen-containing drugs or hormone replacement therapy.


The INR is evaluated in patients treated with oral anticoagulants and its determination serves to monitor dose and dose intervals.


Additional information

Prothrombin time (sec) - PT

Is an important indicator of the condition of the coagulation system. It gives an idea of ​​the activity of the factors involved in the external coagulation pathway (VII, X, V, I, II). Factors VII, X, V, I, II are synthesized in the liver and the process requires the presence of vitamin K.

The assay determines the time (in seconds) during which a thrombus-producing protein called thrombin is produced from inactive prothrombin in the blood plasma taken for analysis.

It can detect both hypercoagulation and hypocoagulation.

Prothrombin time is measured in seconds, but can be expressed in different ways: seconds (sec), prothrombin index in percent (%) and INR (International Normalized Ratio).

Prothrombin index - PI

Prothrombin activity in% is determined by analysis.

International Normalized Ratio (INR)

The study determined the relationship between prothrombin index (PI) and prothrombin time (PT).

It is comparable between different laboratories and according to its importance the doctor can determine the dose of prescribed anticoagulants and the interval between their reception.

INR is useful only in anticoagulant therapy and is not used to diagnose and treat patients with prolonged prothrombin time for other reasons.


How to prepare for the test?

Blood sampling for analysis is necessary without fasting, without taking medication for the last 12 hours. The patient should be informed whether he or she is taking medications that affect blood clotting.

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