Partial Thromboplastin Time

A partial thromboplastin time test can tell you how long it takes for you to make a blood clot. Results from this blood test can tell why your blood is clotting too quickly or too slowly. A PTT test checks many of the proteins or clotting factors that have a part in the clotting process.

Overview

What is a partial thromboplastin time test?

A partial thromboplastin time test or PTT test is a blood test that tells you how long your blood takes to make a blood clot. It takes multiple proteins or clotting factors to complete the clot-making process. If you have an issue with any of these clotting factors, it can affect how long the whole process takes.

Another name for this test is an activated partial thromboplastin time test or aPTT. This is because providers add a substance to your blood sample to activate the clotting process.

A partial thromboplastin time test checks how well most of your clotting factors work. There’s a different test called a prothrombin time test or PT test to check some other clotting factors that the PTT test doesn’t include.

What does a partial thromboplastin time test measure?

A partial thromboplastin time test measures how long it takes your blood to make a clot. It can tell you how much of certain clotting factors you have in your blood. And it can tell you if they’re working right.

When is a partial thromboplastin time test performed?

A healthcare provider may order a partial thromboplastin time test if:

• Your blood is clotting too quickly or too slowly.
• You have a blood clot in a blood vessel.
• You’re bleeding a lot or have a lot of bruises.
• You’ve had miscarriages.
• You have liver disease.
• You’re preparing for a medical procedure or operation and your provider wants to check for bleeding issues.
• You’re getting heparin, a blood thinner, and your provider wants to make sure you’re getting the right dose.
• Your provider needs to know which clotting factors are causing your clotting or bleeding issues.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Test Details

How does a partial thromboplastin time test work?

Once a provider has your blood sample in a lab, they’ll:

1. Separate out the part (plasma) they need.
2. Add an activator to your plasma.
3. Incubate your plasma.
4. Add calcium chloride to complete the activation. This triggers clot formation.

The time it takes (in seconds) for a clot to form is your partial thromboplastin time.

How do I prepare for a partial thromboplastin time test?

You don’t have to do anything to prepare for a partial thromboplastin time test. But drinking a lot of water before your blood draw can make it easier for a provider to find a plump vein to puncture. You may want to wear a shirt with short sleeves so you don’t have to roll up your sleeve.

What should I expect during a partial thromboplastin time test?

A healthcare provider will take a blood sample from your vein. They’ll put it into a tube that has a substance in it to keep it from clotting while it’s in the tube.

The steps a provider will follow are:

1. Ask you to sit with your arm out in front of you. It’ll likely be a special chair with an armrest where you can stretch your arm out.
2. Tie a band around your upper arm.
3. Clean a small area of skin on your arm.
4. Put a small needle into the skin they just cleaned.
5. Use the needle to get blood from your vein and into a tube.

What can I expect after a partial thromboplastin time test?

After a provider takes a blood sample, they’ll:

1. Take the band off your upper arm.
2. Take the needle out of your arm.
3. Press a cotton ball or something similar on the area where they removed the needle.
4. Put a bandage on the area they punctured.

What are the risks of a partial thromboplastin time test?

You’ll feel a quick needle puncture that feels like a pin pricking your skin. You might have a bruise around the area where the needle went into your skin. This should go away in a few days.