Partial Thromboplastin Time

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.

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.

What type of results do you get and what do the results mean?

Partial thromboplastin time test results are the number of seconds your blood needs to make a clot. A clotting time between 25 and 35 seconds is in the partial thromboplastin time normal range. This normal range may vary a bit from lab to lab.

What does it mean when your PTT is high?

If your partial thromboplastin time test result is high, it means your blood is taking longer to clot than it should. This could mean:

• Your heparin dose is too high.
• You have an autoimmune disease that affects clotting.
• You have liver disease.
• You have a type of leukemia that affects clotting.
• You inherited a genetic issue like hemophilia or von Willebrand disease from your parents.
• You don’t have enough vitamin K in your body.

When should I know the results of a partial thromboplastin time test?

It depends on the lab you use. You may get results of a partial thromboplastin time test the same day or in a few days.

If the results are abnormal, what are the next steps?

If you have abnormal results from your partial thromboplastin time test, the next step could be:

• More testing to figure out if you have a specific condition, like an issue with one of your clotting factors.
• A different dose of heparin.

When should I call my doctor?

Contact your healthcare provider if the time frame they gave you for getting your results has come and gone without results. After you have your results, contact your provider if there’s anything that isn’t clear about your results or next steps.

What is the difference between PT and aPTT?

A PT or prothrombin time test checks for different clotting factors than an activated partial thromboplastin time (aPTT or PTT) test. Your provider may order both tests so they can check more clotting factors than they can with just one type of test.

A note from Cleveland Clinic

It can be unsettling to have your blood clotting too quickly or too slowly. A quick blood test can give your provider the answers they need to treat the cause of your clotting issues. Be sure to ask about anything that isn’t clear so your provider can explain it to you.