Prothrombin Time (PT/INR) – BC263
🩸 Coagulation TestReport: Same Day
Sample Type: Blood (Citrated Plasma)
Test Code: BC263
The Prothrombin Time (PT) is a blood test that measures how long it takes for a clot to form in a blood sample. The result is almost always reported along with the INR (International Normalized Ratio), which is a standardized calculation that allows for consistent monitoring of anticoagulant therapy.
✔ The primary test used to monitor the effectiveness of the oral blood thinner Warfarin (Coumadin®).
✔ Helps in diagnosing unexplained bleeding or clotting disorders.
✔ Can be used to assess liver function, as the liver produces clotting factors.
✔ A crucial pre-operative screening test to assess bleeding risk.
Understanding PT and the Crucial INR
Your blood's ability to clot is a complex process involving a series of proteins called clotting factors. The Prothrombin Time test evaluates the "extrinsic pathway" of this cascade, specifically how well factors I, II, V, VII, and X are working. The test measures the time in seconds it takes for your blood plasma to clot after certain reagents are added.
What is INR (International Normalized Ratio)?
The PT result in seconds can vary slightly from one lab to another due to differences in equipment and reagents. To solve this problem, the **INR** was created. The INR is a standardized calculation that adjusts the PT result based on the specific reagents used by the lab. This ensures that a doctor in Delhi can interpret an INR result in exactly the same way as a doctor in New York. For a healthy person not on blood thinners, the INR is typically around 1.0.
Clinical Applications of the PT/INR Test
- Monitoring Warfarin Therapy: This is the most common use. Warfarin is an anticoagulant (blood thinner) prescribed to prevent dangerous blood clots in conditions like atrial fibrillation, deep vein thrombosis (DVT), or after a mechanical heart valve replacement. Doctors use the INR to adjust the warfarin dose to a specific therapeutic range (often an INR of 2.0 to 3.0), which is a delicate balance between preventing clots and avoiding an excessive risk of bleeding.
- Assessing Liver Function: Since the liver produces most of the clotting factors measured by the PT test, severe liver disease can lead to a prolonged PT and an elevated INR. This is an important marker of liver failure.
- Investigating Bleeding Disorders: A prolonged PT/INR can indicate an inherited or acquired deficiency of one of the clotting factors in the extrinsic pathway.
- Checking Vitamin K Status: Vitamin K is essential for the production of several clotting factors. A deficiency can lead to a prolonged PT.
Frequently Asked Questions (FAQ)
If you are taking the blood thinner warfarin, regular monitoring is essential to ensure your dose is correct. The test helps your doctor keep your INR within a specific target range to prevent blood clots without causing dangerous bleeding.
A high INR (e.g., above 3.5) means your blood is clotting too slowly ("too thin"). This increases your risk of bleeding and bruising. Your doctor may need to lower your warfarin dose.
A low INR (e.g., below 2.0 for a person on therapy) means your blood is clotting too quickly ("too thick"). This means you are not adequately protected from forming a dangerous blood clot. Your doctor may need to increase your warfarin dose.
No, fasting is not required for this test. However, it is very important to tell the lab staff about all medications you are taking, especially warfarin or any other blood thinners.