Prothrombin Time (INR) Blood Test
    Prothrombin Time (INR) Blood Test
    Prothrombin Time (INR) Blood Test

Prothrombin Time (INR) Blood Test


A test to measure how long it takes for the blood to clot. Useful for those looking to investigate unusual bleeding, blood clots and those being treated with warfarin.

For this test, you will be required to visit The Doctors Laboratory in London to collect your sample as the sample is not suitable for posting.

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    Visit one of our national clinic partners for a nurse to take your venous blood sample from a vein in your arm. We’ll email you instructions on how to book after we’ve processed your order.
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Biomarker table

Clotting status


Learn more

The international normalised ratio (INR) is a laboratory measurement of how long it takes for blood to form a clot. This can be useful to be able to determine the effects of anticoagulants such as warfarin on the clotting system.
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Who is a Prothrombin Time (INR) Blood Test for?

You can use our PT test if you are being treated with blood-thinning medication (anticoagulant) warfarin (Coumadin®) to monitor your treatment.

What does clotting status mean?

Your clotting cells (platelets) are produced in the bone marrow and help control bleeding. Sometimes too few platelets are produced or are destroyed too quickly, resulting in a condition known as thrombocytopenia. This can be caused by immune disorders, some medication, liver disease, or chronic bleeding. A high platelet count is called thrombocytosis and can be caused by several conditions, including bone marrow disorders, infection and inflammation. Read more about what blood is, the different blood types, and the main functions of blood in our blog: what is blood and what does it do?

What is a Prothrombin Time (INR) Blood Test?

Our Prothrombin Time (INR) Blood Test gives you your international normalized ratio (INR), which is calculated based on the results of your prothrombin time (PT) test. INR is a laboratory measurement of how long it takes for blood to form a clot.

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