Partial Thromboplastin Time (PTT) Test

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 haemophilia.
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 haemophilia 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.

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.

References

American Society of Hematology [Internet]. Washington D.C.: American Society of Hematology; c2018. Bleeding Disorders; [cited 2018 Aug 26]; [about 2 screens]. Available from: http://www.hematology.org/Patients/Bleeding.aspx
Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Hemophilia: Diagnosis; [updated 2011 Sep 13; cited 2018 Aug 26]; [about 3 screens]. Available from: https://www.cdc.gov/ncbddd/hemophilia/diagnosis.html
Hinkle J, Cheever K. Brunner & Suddarth’s Handbook of Laboratory and Diagnostic Tests. 2nd Ed, Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams & Wilkins; c2014. Partial Thromboplastin Time (PTT); p. 400.
Indiana Hemophilia & Thrombosis Center [Internet]. Indianapolis: Indiana Hemophilia & Thrombosis Center Inc.; c2011–2012. Bleeding Disorders; [cited 2018 Aug 26]; [about 3 screens]. Available from: http://www.ihtc.org/patient/blood-disorders/bleeding-disorders
Kids Health from Nemours [Internet]. Jacksonville (FL): The Nemours Foundation; c1995–2018. Blood Test: Partial Thromboplastin Time (PTT); [cited 2018 Aug 26]; [about 3 screens]. Available from: https://kidshealth.org/en/parents/test-ptt.html?ref=search&WT.ac=msh-p-dtop-en-search-cl
Lab Tests Online [Internet]. Washington D.C.; American Association for Clinical Chemistry; c2001–2018. Partial Thromboplastin Time; [updated 2018 Mar 27; cited 2018 Aug 26]; [about 2 screens]. Available from: https://labtestsonline.org/tests/partial-thromboplastin-time-ptt-aptt
Mayo Clinic: Mayo Medical Laboratories [Internet]. Mayo Foundation for Medical Education and Research; c1995–2018. Test ID: ATPTT: Activated Partial Thromboplastin Time (APTT), Plasma: Clinical and Interpretive; [cited 2018 Aug 26]; [about 4 screens]. Available from: https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/40935
National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests; [cited 2018 Aug 26]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
Riley Children’s Health [Internet]. Indianapolis: Riley Hospital for Children at Indiana University Health; c2018. Coagulation Disorders; [cited 2018 Aug 26]; [about 3 screens]. Available from: https://www.rileychildrens.org/health-info/coagulation-disorders
UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida; c2018. Partial thromboplastin time (PTT): Overview; [updated 2018 Aug 26; cited 2018 Aug 26]; [about 2 screens]. Available from: https://ufhealth.org/partial-thromboplastin-time-ptt
University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2018. Health Encyclopedia: Activated Partial Thromboplastin Clotting Time; [cited 2018 Aug 26]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=aptt
UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Partial Thromboplastin Time: Results; [updated 2017 Oct 5; cited 2018 Aug 26]; [about 8 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/partial-thromboplastin-time/hw203152.html#hw203179
UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Partial Thromboplastin Time: Test Overview; [updated 2017 Oct 5; cited 2018 Aug 26]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/partial-thromboplastin-time/hw203152.html
UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Partial Thromboplastin Time: Why It Is Done; [updated 2017 Oct 5; cited 2018 Aug 26]; [about 3 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/partial-thromboplastin-time/hw203152.html#hw203160
WFH: World Federation of Hemophilia [Internet]. Montreal Quebec, Canada: World Federation of Hemophilia; c2018. What is von Willebrand Disease (VWD); [updated 2018 June; cited 2018 Aug 26]; [about 2 screens]. Available from: https://www.wfh.org/en/page.aspx?pid=673