What is a PTT (partial thromboplastin time) test?
A partial thromboplastin time (PTT) test measures the time it takes for a blood clot to form. Normally, when you get a cut or injury that causes bleeding, proteins in your blood called coagulation factors work together to form a blood clot. The clot stops you from losing too much blood.
You have several coagulation factors in your blood. If any factors are missing or defective, it can take longer than normal for blood to clot. In some cases, this causes heavy, uncontrolled bleeding. A PTT test checks the function of specific coagulation factors. These include factors known as factor VIII, factor IX, factor X1, and factor XII.
Other names: activated partial thromboplastin time, aPTT, intrinsic pathway coagulation factor profile
What is it used for?
A PTT test is used to:
- Check the function of specific coagulation factors. If any of these factors are missing or defective, it can mean you have a bleeding disorder. Bleeding disorders are a group of rare conditions in which blood doesn’t clot normally. The most well-known bleeding disorder is hemophilia.
- Find out if there is another reason for excessive bleeding or other clotting problems. These include certain autoimmune diseases that cause the immune system to attack coagulation factors.
- Monitor people taking heparin, a type of medicine that prevents clotting. In some bleeding disorders, the blood clots too much, rather than too little. This can cause heart attacks, strokes, and other life-threatening conditions. But taking too much heparin can cause excessive and dangerous bleeding.
Why do I need a PTT test?
You may need a PTT test if you:
- Have unexplained heavy bleeding
- Bruise easily
- Have a blood clot in a vein or artery
- Have liver disease, which can sometimes cause problems with blood clotting
- Will be getting surgery. Surgery can cause blood loss, so it’s important to know if you have a clotting problem.
- Have had multiple miscarriages
- Are taking heparin
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. If your results show that your blood took a longer-than-normal time to clot, it may mean you have:
- A bleeding disorder, such as hemophilia or von Willebrand disease. Von Willebrand disease is the most common bleeding disorder, but it usually causes milder symptoms than other bleeding disorders.
- Liver disease
- Antiphospholipid antibody syndrome or lupus anticoagulant syndrome. These are autoimmune diseases that cause your immune system to attack your coagulation factors.
- Vitamin K deficiency. Vitamin K plays an important role in forming coagulation factors.
If you are taking heparin, your results can help show whether you are taking the right dose. You will probably be tested on a regular basis to make sure your dosage stays at the right level.
If you are diagnosed with a bleeding disorder, talk to your health care provider. While there is no cure for most bleeding disorders, there are treatments available that can help manage your condition.
Is there anything else I need to know about a PTT test?
A PTT test is often ordered along with another blood test called prothrombin time. A prothrombin time test is another way to measure clotting ability.