1100. Prothrombin time (PT, % by Quick, INR)

A prothrombin time (PT) test is a comprehensive analysis necessary for assessing the extrinsic pathway of blood coagulation. It includes determination of prothrombin time (PT), Quick prothrombin percentage, and international normalized ratio (INR/INR). The test is used to diagnose thrombosis and disseminated intravascular coagulation (DIC), to determine the risk of developing various blood and cardiovascular diseases, and to assess a person's condition preoperatively and postoperatively.

The blood coagulation system is a complex, multicomponent mechanism activated in response to vascular injury. The prothrombin time (PT) test assesses the activity of the so-called extrinsic coagulation pathway, which depends on the presence of coagulation factors II (prothrombin), V, VII, and X, fibrinogen, and calcium.

Test parameters:

• Prothrombin time (PT) – the time (in seconds) that reflects the plasma clotting time after the addition of a thromboplastin-calcium mixture. An increase in this time indicates a deficiency of coagulation factors or the presence of anticoagulants.
• Quick prothrombin (%) – expresses the activity of the prothrombin complex as a percentage. A significant decrease indicates a high risk of bleeding.
• The International Normalized Ratio (INR) is a standardized method for presenting prothrombin time (PT) test results, specifically developed and recommended for monitoring indirect anticoagulant therapy by the WHO Expert Committee, the International Committee for the Study of Thrombosis and Haemostasis, and the International Committee for Standardization in Haematology. INR is calculated using the formula: INR = (Patient's Prothrombin Time / Normal Mean Prothrombin Time) x ISI (International Sensitivity Index), a measure of the sensitivity of the thromboplastin used, standardizing it relative to an international standard.

This test is sensitive to bleeding disorders caused by vitamin K deficiency, liver disease, and hereditary coagulopathies. It allows for monitoring the effectiveness of anticoagulant therapy and assessing the risk of bleeding before surgery.

When?

• During preparation for elective or emergency surgery.
• Before starting anticoagulant treatment.
• To monitor treatment with indirect anticoagulants.
• To screen for blood coagulation disorders caused by prothrombin complex factor deficiency.
• If vitamin K deficiency is suspected.
• To diagnose coagulopathies, particularly hypo- or hypercoagulable states.
• If DIC is suspected.
• For dysfibrinogenemia.
• To assess liver protein-synthetic function (additional test).

Who should use it?

• Pregnant women with coagulation disorders or gestosis, to monitor their condition.
• Patients with thrombosis, embolism, or recurrent miscarriages.
• Individuals with suspected bleeding disorders requiring diagnosis and treatment monitoring.
• Patients requiring evaluation of coagulation inhibitors (vaginal antibodies or others).

• Venous blood

In order to exclude factors that may affect the test results, we recommend to follow the preparation rules: