PT INR: What is the Prothrombin Time Test and Why is it Important?

The PT INR (Prothrombin Time Test) is a blood test that measures how long it takes for your blood to clot. Learn more about this important test and why it’s necessary.

The PT INR Test  is a common blood test that measures the time it takes for your blood to clot. This test is important because it can help diagnose and monitor conditions that affect blood clotting, such as liver disease, bleeding disorders, and the use of blood-thinning medications. Learn more about the Prothrombin Time Test and why it’s necessary.

Prothrombin time PT INR test

The prothrombin time (PT) examination gauges the duration required for a blood sample to coagulate. INR (international normalized ratio) represents a method of computation derived from the outcomes of a PT test.

If your blood clots too quickly, it could increase your risk for blood clots and related health issues. Therefore, it is important to maintain a proper balance of clotting factors for optimal health. The liver produces a type of protein called Prothrombin which is classified as one of many coagulation factors responsible for forming a blood clot when your body experiences bleeding from cuts or any other injury.

The speed at which the clotting occurs depends on the amount and efficiency of the clotting factors present in the bloodstream. Deficiency in these factors may lead to slow clot formation while an excess can increase the risk of developing problems associated with blood clots. Hence, it is crucial to maintain an appropriate balance of these coagulation agents for maintaining good health., you may bleed too much after an injury. If your blood clots too fast, dangerous clots may form in your arteries or veins.

Other names: PT Test, PT INR Test, Pro test, INR (International Normalized Ratio) Test, Coagulation Test, Clotting Time Test

What is PT INR Test used for?

The Prothrombin Time Test is often used to:

  • Monitor the effectiveness of blood-thinning medications, such as warfarin.
  • Diagnose and monitor conditions that affect blood clotting, such as liver disease and bleeding disorders.
  • Determine the cause of unusual blood clotting.
  • Determine the cause of abnormal bleeding.
  • Pinpointing the reason for unexpected bruising or bleeding.
  • Assessing the potential for pregnant women to bleed.
  • Measuring how helpful vitamin K therapy is.
  • Before the surgical procedure, it is necessary to assess the blood’s ability to clot

Commonly, a medical professional will administer both a PT INR test and a PTT test to determine if there are any clotting issues present in a patient. The PTT test is also utilized to check for any coagulation complications.



The process MMis an uncomplicated blood test used for diagnosis. The following are the steps involved in extracting a blood sample from a vein in your arm or hand:

  • Firstly, a technician specialized in drawing blood (phlebotomist) may use an elastic band called a tourniquet to wrap around your arm.
  • The phlebotomist would then locate the vein that contains blood.
  • Once found, the area is cleansed with alcohol.
  • A needle is carefully inserted into the vein to draw out the blood sample which will be taken up by either a syringe or a small vial.
  • Before finishing the procedure, cotton is applied to the puncture site, gently pressing down until the bleeding stops.
  • Then, a small band-aid is placed on the same spot which can be removed after an hour.
  • The entire process should take only a few minutes to complete.


In case you used to take warfarin, you might have to delay your everyday intake until after completing a test. Your healthcare professional will provide further instructions on the necessary actions to be taken.

“Related: Renin Blood Test, Everything You Need to Know this test

Risks of the test

The test is uncomplicated and poses a low risk, similar to any other blood examination. Possible dangers consist of:

  • Infection if the needle is contaminated and protocols are not followed, but this happens rarely.
  • If the blood vessel is difficult to find, it may cause multiple needle pricks.
  • Those taking blood thinners or with bleeding disorders should inform their healthcare provider as it may result in excessive bleeding at the puncture site.

Results interpretation

Usually, the results of the Prothrombin Time (PT) test are reported as an International Normalised Ratio (INR). The INR is calculated using a formula provided by the World Health Organization (WHO), which involves dividing the patient’s PT by a standardised control PT value for the test (INR = Patient PT ÷ Control PT).

The Normal values for INR are approximately from 0.8 to 1.1, and for PT, they fall in the range of 11 to 13.5 seconds.

In case of Warfarin therapy

  • If your INR levels are insufficiently low, it could put you in danger of developing hazardous blood clots.
  • Elevated INR levels can increase the likelihood of hazardous bleeding, indicating a potential risk to your health.
  • To minimize these dangers, your medical professional may alter the amount of warfarin you are taking.

In case of no Warfarin therapy

  • If the INR level is higher than usual, it suggests that blood clotting is slower than normal. This condition can be precarious because it may indicate a risk of bleeding due to various cases such as:
    • Liver disease
    • Paucity of vitamin K
    • Treatment with warfarin.
    • Disseminated intravascular coagulation (DIC).
    • Inherited bleeding ailments like haemophilia.
  • If the INR is low, it indicates that the blood is clotting too rapidly, which could indicate a danger of blood clots. Several conditions might result in a lack of clotting factors including:
    • Deep vein thrombosis (DVT).
    • Pulmonary embolism (PE).
    • Atrial fibrillation.
    • Antiphospholipid syndrome (APLA Test)
    • Liver disease.

Related tests

  • Partial Thromboplastin Time (PTT) Test
  • Aspartate Aminotransferase (AST)
  • Alanine Aminotransferase (ALT)
  • D-Dimer Test
  • Platelet Tests

We hope this article has provided you with a better understanding of the Prothrombin Time Test and its importance in diagnosing blood clotting disorders. It’s always important to stay on top of your health and to visit your healthcare provider with any concerns. To learn more about the Prothrombin Time Test or to share your own experiences, please leave a comment below. Thank you for reading.

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