PT

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Also known as: Prothrombin Time; PT
Formal name: Prothrombin Time

At a Glance

Why Get Tested?

To help diagnose a bleeding disorder; to help estimate the severity of liver disease. A tightly controlled version of the PT called the International Normalised Ratio (INR) is used to measure the effect of anticoagulant drugs such as warfarin.

When to Get Tested?

No test preparation is needed. If the patient is receiving anticoagulant therapy, the specimen should be collected before the daily dose is taken. It is essential the blood is taken quickly and smoothly and that the anticoagulant bottle is filled exactly to the designated mark or the result may be inaccurate.

Sample Required?

A blood sample taken from a vein in the arm

Test Preparation Needed?

None needed, although if you are receiving anticoagulant therapy, the sample should be collected before taking your daily dose.

The Test Sample

What is being tested?

The test measures how long it takes for your blood to begin to form clots. Prothrombin is a plasma protein produced by the liver. Clotting is caused by a series of clotting factors which activate each other, including the conversion of prothrombin to thrombin. The test used to measure the activity of this clotting factor is called the prothrombin time, or PT.

How is the sample collected for testing?

Blood is collected by needle from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. If the patient is receiving anticoagulant therapy, the specimen should be collected before the daily dose is taken. It is essential the blood is taken quickly and smoothly and that the anticoagulant bottle is filled exactly to the designated mark or the result may be inaccurate.

The Test

Common Questions

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.