Blood
Partial Thromboplastin Time (PTT)
Also known as: aPTT, APTT, Activated Partial Thromboplastin Time
Reference ranges by source
Published adult intervals: 3, from 3 named sources, shown in sec.
About Partial Thromboplastin Time (PTT)
A partial thromboplastin time (PTT) test uses a blood sample to measure how long it takes for your blood to make a clot. Normally, when you get a cut or injury that causes bleeding, many different types of proteins in your blood work together to make a clot to stop the bleeding. These proteins are called coagulation factors or clotting factors.
If any of your clotting factors are missing, at a low level, or not working properly, your blood may not clot the way it should.
A PTT test helps check a specific group of clotting factors. It works as a screening test for problems in the intrinsic clotting pathway (factors VIII, IX, XI, and XII) and the common pathway (factors II, V, X, and fibrinogen), and it can also pick up on substances in the blood that block these factors from working. A PTT test is often done with other tests that check clotting factors and how well they all work together.
Main source: MedlinePlus ↗
Useful for
Find the cause of too much bruising or bleeding.
Find the cause of clotting problems. Causes can include certain autoimmune diseases such as lupus and antiphospholipid syndrome (APS).
Screen for low levels or inhibitors of the clotting factors that the test covers, which can lead to bleeding or clotting problems.
Monitor people taking heparin, a type of medicine that's used to prevent and treat blood clots. PTT testing can help make sure the dose is safe and effective.
Check the risk for possible bleeding problems before surgery or medical procedures. (A PTT test is not always used as a routine test before surgery. It may be used for certain people who may have a risk for bleeding problems.)
Main source: MedlinePlus ↗
Interpretation
Your PTT test results will show how much time it took for your blood to clot. Results are usually given as a number of seconds. A PTT test is often ordered along with another blood test called a prothrombin time (PT) test. A PT test measures other clotting factors that a PTT test doesn't check. Your provider will usually compare the results of both tests to understand how your blood is clotting. Ask your provider to explain what your test results mean for your health.
If your blood took longer than normal to clot, or if it clotted faster than normal, it may be a sign of a problem with your clotting factors. Talk with your provider to learn what your test results mean.
For general wellness information only. Talk to a clinician about your specific results.
Main source: MedlinePlus ↗
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Sources
Last updated 2026-05-02
This page presents source-specific reference data and sourced explanations. For general wellness information only. This is not medical advice. For diagnosis or treatment of any condition, talk to a qualified clinician.