Prothrombin Time

Other names: PT; Pro Time

The PT test measures the amount of time it takes the body to form blood clots. Prothrombin is a form of plasma protein, which is produced by the liver. During the clotting process, prothrombin is converted into thrombin.

When is the test used?

The test is used to check the body’s ability to form blood clots; it is most commonly used to monitor the condition of a patient who is receiving anticoagulant therapy (such as warfarin). Anticoagulant medications help to prevent the formation of blood clots.

The test is usually carried out on patients who are taking anticoagulant medication but it may be used occasionally for patients who are about to have surgery or those with suspected bleeding or liver disorders.

How is the test performed?

The test is done by taking a sample of blood from a vein in the patient’s arm; a needle in inserted into the vein and the blood is collected in a syringe. Once the sample has been collected, the blood will be placed in a sample bottle, labelled with the patient’s name and sent away to the laboratory for evaluation.

What do the test results mean?

The test results will show the PT; if this is within the target INR (International Normalized Ratio), this means they are receiving the correct dose of anticoagulant. If the PT or the INR is high, this means that the body is taking too long to form blood clots and the dose may be increased.

Some medications and substances, including alcohol, can interfere with the test results; drugs including antibiotics and aspirin may cause PT to increase, while barbiturates and oral contraceptives may cause PT to decrease. It is important that the patient discusses any medication they are taking with their doctor before they have the test done.

Specific Blood Tests

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