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Blood Test: Prothrombin Time (PT)

Medically reviewed by: Larissa Hirsch, MD

What Is a Blood Test?

By taking and testing a small sample of a person’s blood, doctors can check for many kinds of diseases and conditions. Blood tests help doctors check how the body’s organs are working and see if medical treatments are helpful.

To help your child get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is anxious about it, work together on ways to stay calm.

What Is a Prothrombin Time Test?

A prothrombin time (PT) test measures how long it takes for a clot to form in a blood sample. Clotting is important to help prevent too much bleeding. Proteins called clotting factors are needed for blood to clot properly. If there aren't enough of them, or any of them don't work as they should, it can take longer than normal for blood to clot.

Why Are PT Tests Done?

Doctors do PT tests to check for bleeding problems. A child might have the test if they’ve had a lot of bleeding or bruising, have a medical condition that can lead to problems with clotting, or are having surgery or a procedure that might cause bleeding. Doctors also do PT tests to follow clotting levels in children who are on blood-thinning medicines.

What if I Have Questions?

If you have questions about the PT test or what the test results mean, talk to your doctor. 

Medically reviewed by: Larissa Hirsch, MD
Date reviewed: September 2021