Partial Thromboplastin Time (PTT) Test

What is a PTT (partial thromboplastin time) test?

A partial thromboplastin time (PTT) test uses a blood sample to measure the number of seconds it takes for your blood to 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, and your liver makes most of them.

If any of your clotting factors are missing, at a low level, or not working properly, your blood may:

• Clot too slowly after an injury or surgery. If this happens, you may have a bleeding disorder, such as hemophilia. These disorders can cause serious blood loss after an injury.
• Clot too much and/or too quickly, even without an injury. This may lead to unnecessary clots that block your blood flow and cause serious conditions, such as heart attack, stroke, or clots in the lungs.

A PTT test helps check how many of a specific group of clotting factors you have and how well they’re working. If the blood in your sample takes longer than usual to clot, it may mean your body isn’t making enough of these clotting factors.

To get a more complete understanding of your blood’s ability to make a clot, your health care provider may order other tests alongside a PTT test. The most common of these is 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.

Other names: activated partial thromboplastin time, aPTT, intrinsic pathway coagulation factor profile

What is it used for?

A PTT test is used to check for problems with a specific group of blood clotting factors. It's done to:

• Find the cause of too much bruising or bleeding. For example, your provider may use this test to help diagnose a bleeding disorder such as hemophilia.
• 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 for the risk of any bleeding problems. This test is often only used if you are at high risk of bleeding problems.
• Check for clotting problems related to autoimmune diseases such as lupus and antiphospholipid syndrome (APS). These diseases cause your body to make proteins called autoantibodies. Autoantibodies, unlike antibodies (which attack germs that could make you sick), attack your own healthy tissues.

Why do I need a PTT test?

You may need a PTT test if you have:

• Problems with bleeding or bruising and the cause is not known.
• A blood clot in a vein or artery.
• Liver disease. This condition can affect your body’s ability to form blood clots.
• A history of several miscarriages, which can be caused by clotting issues.
• A bleeding or clotting disorder and don’t know which clotting factors are involved.
• Surgery scheduled and you have a history of excessive bleeding (including nose bleeds and easy bruising).
• Signs of an autoimmune condition that can cause clotting problems.

Your provider may also order a PTT test if you’re taking heparin. With the results of this test, your provider will be able to ensure it’s a safe and effective dose.

Lastly, your provider may order this test if you have symptoms suggesting a clotting disorder such as:

• Bleeding for a long time after minor cuts
• Joint pain or swelling
• Signs of excessive clotting such as pain, swelling, or warmth in your arms or legs

What happens during a PTT test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a PTT test.

Are there any risks to the test?

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.

What do the results mean?

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.

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.
• Liver disease.
• A lack of vitamin K.
• Certain genetic disorders that you inherit. That means that your parents passed the gene to you. These disorders affect certain clotting factors and increase your risk of bleeding. They include Von Willebrand disease and hemophilia.
• Too much heparin.
• Certain types of leukemia.
• Autoimmune diseases, such as lupus anticoagulant syndrome.

Autoimmune diseases can affect your PTT test results by showing a slower clotting time than you actually have. That’s because the chemicals in the PTT test react with the autoantibodies in your blood sample. This reaction causes your blood sample to clot more slowly than the blood in your body. If your provider thinks that an autoimmune disease is causing a clotting problem, they will usually order more tests to make a diagnosis.

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). This rare but serious condition may develop if you have an infection or damage to organs or tissues that affects blood clotting. In the early stage, you have too much blood clotting. Later on, DIC starts to use up clotting factors in your blood, which leads to bleeding problems.
• High levels of clotting factors, such as during inflammation, pregnancy, or cancer.
• Cancer of the ovaries, colon, or pancreas that is advanced, which means the cancer has spread to other parts of the body and is unlikely to be controlled with treatment.

Even if your sample clotted faster or slower than usual, that doesn’t necessarily mean you have a medical condition. This is because there can be a difference between how fast your blood clots in a test setting and how fast it clots in your body. Because of this, if your results are unusual, your provider may order more tests.

Talk with your provider to learn what your test results mean for you.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a PTT test?

If your provider thinks you may have a clotting disorder linked to lupus, you may have a test called an LA-PTT. This is a type of PTT test that looks for a protein that's linked to increased clotting and having many miscarriages.