Prothrombin Time (PT)

Prothrombin time (PT) is a blood test that measures the time it considers the liquid portion (plasma) of your blood to embolisms.

An associated blood test is partial thromboplastin time (PTT).

The prothrombin time (PT) — along with its derived measures of prothrombin ratio (PR) and international normalized ratio (INR) — are assays evaluating the extrinsic pathway of coagulation. This test is also called “ProTime INR” and “PT/INR” (Wikipedia)

Normal Prothrombin Time (PT) Results

PT is measured in seconds. The majority of the time, outcomes are offered as what is called INR (global stabilized ratio).

If you are not taking blood thinning medications, such as warfarin, the typical variety for your PT results is:

  • 11 to 13.5 seconds
  • INR of 0.8 to 1.1

If you are taking warfarin to prevent embolism, your doctor will most likely choose to keep your INR in between 2.0 and 3.0.

Ask your doctor what outcome is right for you.

Regular value ranges may vary a little among various labs. Some labs use different measurements or test different samples. Speak with your doctor about the meaning of your particular test outcomes

What Abnormal Results Mean

If you are not taking blood thinning medications, such as warfarin, an INR result above 1.1 methods your blood is clotting more slowly than normal. This may be due to:

  • Bleeding conditions, a group of conditions where there is a problem with the body’s blood clotting procedure.
  • Condition in which the proteins that control blood clotting ended up being over active (distributed intravascular coagulation).
  • Liver disease.
  • Low level of vitamin K.

If you are taking warfarin to avoid embolisms your doctor will more than likely choose to keep your INR between 2.0 and 3.0:

  • Depending on why you are taking the blood thinner, the preferred level may be various.
  • Even when your INR remains between 2.0 and 3.0, you are most likely to have bleeding issues.
  • INR results greater than 3.0 may put you at even higher risk for bleeding.
  • INR results lower than 2.0 might put you at risk for establishing a blood clot.

A PT result that is too high or too low in somebody who is taking warfarin (Coumadin) might be due to:

  • The incorrect dosage of medicine.
  • Drinking alcohol.
  • Taking certain over the counter (OTC) medications, vitamins, supplements, cold medications, antibiotics, or other medications.
  • Eating food that alters the way the blood-thinning medicine works in your body.

Your supplier will teach you about taking warfarin (Coumadin) the appropriate method.

How a Prothrombin Time Test is Performed

A blood sample is required. If you are taking ant blood-thinning medications, you will be watched for signs of bleeding.

How to Prepare for the Test

Particular medicines can change blood test outcomes.

  • Your health care company will inform you if you have to stop taking any medicines before you have this test. This might include aspirin, heparin, antihistamines, and vitamin C.
  • DO NOT stop or change your medicines without speaking with your doctor first.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel just a prick or stinging. Afterward, there might be some throbbing or slight bruising. This quickly goes away.

Why the Test is Performed

The most typical need to perform this test is to monitor your levels when you are taking a blood-thinning medication called warfarin. You are most likely taking this medication to avoid embolism.

Your company will examine your PT regularly.

You may also require this test to:

  • Find the reason for abnormal bleeding or bruising
  • Inspect how well your liver is working
  • Try to find signs of a blood clotting or bleeding condition


This test is frequently done on people who may have bleeding problems. Their risk of bleeding is slightly greater than for people without bleeding issues.

Other slight risks can include:

  • Passing out or feeling lightheaded.
  • Hematoma (blood accumulating under the skin).
  • Infection (a slight risk whenever the skin is broken).
  • Several leaks to locate veins.

Alternative Names: PT; Pro-time; Anticoagulant-prothrombin time; Clotting time: protime; INR; International stabilized ratio.

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