Prothrombin Time with INR

This test may help measure how long it takes for your blood to clot. A healthcare provider may use this to monitor medication in your blood if you are taking warfarin (a type of medication known as a blood thinner which can treat and prevent blood clots). Read more

Test details

Sample type:

Blood

Preparation:

You do not need to do anything special to prepare for the sample collection. This test does not require fasting.

Test type: In Person

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$39.00

+ $6.00 Physician Service Fee

Quantity

What

Our PT/INR Test measures how long it takes for blood to clot.

Who

Must be 18+ years of age to purchase.

How

Blood

Where

Find a location near you

Schedule an appointment, then visit a Quest Diagnostics patient service center location.

About the Test

Our Prothrombin Time with INR (PT/INR) Test measures how long it takes for your blood to form a clot (coagulate). Anticoagulants (anti-clotting medications) change the way your blood clots. Warfarin is a commonly prescribed anticoagulant, or blood thinner, that prevents blood from clotting. Anticoagulant therapy must be carefully monitored to make sure the dosage is right for the patient; otherwise, severe and persistent bleeding or excessive blood clotting (hypercoagulation) can occur.

Coagulation is the process by which a blood clot is formed, and it involves multiple substances in the body called clotting factors. This process requires prothrombin, a blood protein produced in the liver that is needed for the normal clotting of the blood. A PT (prothrombin time) test is a blood test used to measure how long it takes your blood to clot. PT test results are often presented as a ratio known as INR (international normalized ratio). The INR is a standardized value that is consistent across all laboratories worldwide. This means your INR value has a scale that is accepted and understood by all healthcare professionals.

The body’s natural reaction to form blood clots to stop bleeding is a healthy response when there is damage to a blood vessel. Your body protects itself from excessive bleeding by forming a clot to seal over an injury. Blood clots can also form when they aren’t needed and cause serious medical issues like a heart attack or stroke. Blood clots can be dangerous; anticoagulants (anti-clotting medications) may be used to treat and prevent blood clots from forming in the blood vessels and heart. Warfarin (also known as a blood thinner) is an anticoagulant medication that makes the blood less likely to form clots by blocking the formation of vitamin K–dependent clotting factors. Vitamin K is needed to help your blood clot and prevent bleeding. Warfarin interferes with vitamin K and makes your blood clot more slowly.

If you are taking warfarin to prevent blood clots from forming, a PT/INR Test may be recommended to check whether the medication is working. If you are not taking blood thinning medication, a PT/INR Test may also be used to check for bleeding or clotting disorders, vitamin K deficiency (low levels of vitamin K in the blood), or liver disease.

You must be 18 years of age or older to purchase. Purchases not permitted in: AK, AZ, HI.

You do not need to do anything special to prepare for the sample collection. This test does not require fasting.

When your results are ready, we will send them to you in a clear, easy-to-read report.

You will have the option to speak with an independent physician to discuss your results.

If your results differ from expected ranges, you may receive an alert call to inform you.

Your test results will be available to you a few days after we collect your sample.

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After your purchase, schedule an appointment at a nearby Quest Diagnostics location and have your specimen sample collected by a trained healthcare professional.

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Access test results from your phone as soon as they’re available, with the option to discuss your results with an independent physician at no extra cost.

Your results are available on our free, secure patient portal that you can access on your smartphone, tablet, or desktop. You will receive an email notification when your results are ready. You can also share your results with your healthcare provider, family, or friends.

FAQs

Are there other names for this test?

Yes, this test is also called PT with INR, protime INR, protime with INR, and prothrombin time/international normalized ratio.

Are anticoagulants and blood thinners the same?

Anticoagulants are often called blood thinners, but do not actually change the consistency of the blood. These medications make it harder for blood clots to form in the heart, veins, and arteries and help prevent existing clots from getting larger. Antiplatelets like aspirin are another type of blood thinner which helps prevent platelets from clotting and are usually given to people with a history of heart attack or stroke.

Why is warfarin called a vitamin K antagonist?

Vitamin K helps the body create blood clots and slow bleeding. Warfarin functions as a vitamin K antagonist (blocker) by interfering with the liver's conversion of vitamin K, causing the blood to clot more slowly.

What should I do if my PT/INR level is out of range?

If your test result is showing lower or elevated PT/INR values, you should contact your healthcare provider right away to establish next steps of care.

Prothrombin Time with INR