Also called: aPTT, Activated Partial Thromboplastin Time

Partial Thromboplastin Time (PTT) Blood Test

What Is a Partial Thromboplastin Time Test?

A partial thromboplastin time (PTT) 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.

Thromboplastin (throm-​bo-​PLAS-​tin) is a protein that activates clotting. A prothrombin time (PT) blood test uses thromboplastin to check for some clotting factors, while the PTT test uses part of thromboplastin to check for others. That’s why the PTT test is called “partial.” The tests are often done together.

Why Are Partial Thromboplastin Time Tests Done?

Doctors do PTT tests to check for bleeding problems. Kids might have the test if they:

• have had a lot of bleeding or bruising
• have a medical condition that can lead to problems with clotting
• are having surgery or a procedure that might cause bleeding

Doctors also do PTT tests to follow clotting levels in kids who are on blood-thinning medicines.

Top Things to Know

• The partial thromboplastin time (PTT) blood test checks the time it takes for blood to start clotting.
• Doctors use it to check for bleeding or clotting problems and see if blood-thinning medicine is working.
• Kids might need to stop taking certain medicines or not eat or drink before the blood test.
• Your doctor can explain what it means if PTT is low or high.

How Can I Help My Child Prepare for a Blood Test?

To help kids 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 nervous about it, work together on ways to stay calm. Deep breathing or even imagining being in a place that makes your child feel safe and relaxed can help.

What Do Partial Thromboplastin Time Test Results Mean?

Your doctor will explain what the results of the PTT test mean for your child. The “normal” range of PTT varies based on things like age and gender.

High Partial Thromboplastin Time

Elevated PTT, or high PTT, means that blood is taking longer than usual to clot. This could be due to things like:

• blood-thinning medicine
• a bleeding or blood clotting condition, or other blood disorder
• a liver problem
• too little vitamin K
• not getting enough nutrition from food

Low Partial Thromboplastin Time

Low PTT means that blood is clotting faster than usual. This could be due to a clotting problem, inflammation, or an injury.

What Else Should I Know?

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