Partial Thromboplastin Time (PTT) Test
Reviewed
Also called: activated partial thromboplastin time, aPTT, intrinsic pathway coagulation factor profile
A partial thromboplastin time (PTT) test uses a blood sample to measure the number of seconds it takes for your blood to clot.
Specimen: blood sample from a vein in your arm
Why this test may be ordered
- Problems with bleeding or bruising and the cause is not known
- A blood clot in a vein or artery
- Liver disease
- A history of several miscarriages
- A bleeding or clotting disorder and you don’t know which clotting factors are involved
Preparation and collection
You don't need any special preparations for a PTT test.
A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
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. You may also see the results of a PT test alongside your PTT test results.
- Blood took longer than normal to clot: In general, if your blood took longer than normal to clot on a PTT test, it may be a sign of: Hemophilia A or B. Certain genetic disorders that you inherit. These disorders affect certain clotting factors and increase your risk of bleeding. Certain types of leukemia. Limitation: Autoimmune diseases can affect your PTT test results by showing a slower clotting time than you actually have. Next step: If your provider thinks that an autoimmune disease is causing a clotting problem, they will usually order more tests to make a diagnosis.
- Blood clotted faster than normal: If your blood clotted faster than normal on a PTT test, it may be a sign of: The early stage of disseminated intravascular coagulation (DIC). High levels of clotting factors, such as during inflammation, pregnancy, or cancer. Limitation: A PT test measures other clotting factors that a PTT test doesn't check. Next step: Your provider will usually compare the results of both tests to understand how your blood is clotting.
- There can be a difference between how fast your blood clots in a test setting and how fast it clots in your body.
- Autoimmune diseases can affect your PTT test results by showing a slower clotting time than you actually have.
- Even if your sample clotted faster or slower than usual, that doesn’t necessarily mean you have a medical condition.
What to do next
Your provider will usually compare the results of both tests to understand how your blood is clotting.
- What do my PTT test results mean for me?
- Do I need any follow-up tests based on my results?
- Should I be concerned about bleeding or clotting risks?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Partial Thromboplastin Time (PTT) Test