Patient education: Partial thromboplastin time test (The Basics)

What is a partial thromboplastin time test? — This is a blood test that measures how long it takes blood to clot. It is also called a "PTT" test. Some people use the term "activated PTT" or "aPTT" test.

A PTT test checks whether your blood clots normally. If clotting is not normal, additional tests are needed to understand why. Possible reasons for abnormal clotting include:

●Not having enough of certain proteins that help blood to clot

●Taking medicines to prevent blood clots

●A condition called "antiphospholipid syndrome"

Your PTT tells your doctor if your blood is clotting normally. The other main clotting test is called "prothrombin time," or "PT."

Why might I get a PTT test? — Your doctor or nurse might want you to have a PTT test:

●If you have abnormal bleeding – This might include heavy menstrual periods, nosebleeds, bleeding gums, or blood in your urine or bowel movements.

●If you have a condition that could affect how your blood clots, such as liver disease

●If you are having surgery (but not everyone having surgery needs this test)

●Before you start taking an anti-clotting medicine – These medicines are sometimes called "blood thinners."

●To monitor you if you already take certain anti-clotting medicines

Your doctor might order other tests to check blood clotting, too.

How do I prepare for a PTT test? — For this test, you need to get a "blood draw." Your doctor or nurse will tell you where to go for this.

It might help to wear a short-sleeve shirt to your blood draw appointment. This makes it easier for the person drawing your blood to get to your arm.

What happens during a blood draw? — For the blood draw, a needle is used to take a small amount of blood from your arm (figure 1). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Most of the time, getting blood taken does not cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

Your PTT test result will tell you how long it took for your blood to clot, for example, 30 seconds.

If your PTT test shows any abnormal results, your doctor or nurse will talk to you about what to do next. They might need to repeat the test or do more tests to figure out what the cause is.

If you do have a health problem, your doctor will work with you to come up with a plan for treatment.

More on this topic

Patient education: Prothrombin time and INR (PT/INR) (The Basics)
Patient education: Taking oral medicines for blood clots (The Basics)
Patient education: Managing increased bleeding risk (The Basics)
Patient education: Factor V Leiden (The Basics)

Patient education: Antiphospholipid syndrome (Beyond the Basics)