Prothrombin Time with INR 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.

No doctor’s visit needed.

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.

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