What is the Partial Thromboplastin Time?

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  • Written By: Dulce Corazon
  • Edited By: W. Everett
  • Last Modified Date: 23 November 2019
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Partial thromboplastin time (PTT) test is a type of blood test usually done to check patients for possible bleeding problems and to monitor patients taking anticoaguants. It is also often performed to evaluate patients who are about to have surgery in order to prevent bleeding complications during the operation. Sometimes referred to as activated partial thromboplastin time (aPTT), this test measures the duration of time for a blood clot to form.

The normal result for partial thromboplastin time test is usually between 30 to 45 seconds. This may sometimes vary among laboratories, depending on the methods they use. Those who are taking anticoagulants often have a longer clotting time, approximately two times longer than those who do not. Other diseases also associated with longer partial thromboplastin time include liver disease, Vitamin K deficiency, and kidney disorders. A longer clotting time is also an indication of clotting factor deficiency.


There are about 13 blood clotting factors, usually referred to as factor 1, factor 2 and so on, and they are mostly made up of proteins acting in a sequential pattern in order to form a clot. Patients with bleeding problems, such as hemophilia and hypofibrinogenemia, commonly have deficiencies or defects in one of their blood clotting factors. Hemophilia is a hereditary disease in which people usually lack either factor 8 or factor 9. Hypofibrinogenemia is another inherited disease caused by a lack of factor 1. In both conditions, there is the tendency for patients to bleed longer and lose large amounts of blood in cases of injury and trauma.

Patients with deep vein thrombosis and myocardial infarction are frequently given anticoagulants for treatment. Deep vein thrombosis is the formation of clots in the blood vessels of the leg, often resulting in pain and swelling of the affected area. Myocardial infarction or heart attack usually occurs when a blood vessel delivering blood to the heart muscles is blocked by a clot. In these patients, partial thromboplastin time tests are usually done regularly to monitor these patients and to check if the dose of medicine given is appropriate.

Another test, called prothrombin time (PT), is also often done together with the partial thromboplastin time test. Both tests are generally done in the laboratory after a technician draws a blood sample from the patient. Risks associated with the process of taking blood samples include infection at the area of injection, slight pain, throbbing, and lightheadedness.


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