aPTT, also known as Activated Partial Thromboplastin Time, is a medical test that measures the time it takes for blood to clot. This test is used to diagnose bleeding disorders and monitor the effects of anticoagulant therapy, such as warfarin (Coumadin) or heparin.

Why is aPTT Test Performed?

The aPTT test is performed to evaluate the function of the clotting system in the body. This test helps to diagnose bleeding disorders, such as hemophilia and von Willebrand disease, which are caused by a deficiency or dysfunction of certain clotting factors.

It is also used to monitor the effectiveness of anticoagulant therapy, which is used to prevent blood clots from forming in the body. This type of therapy is commonly used to treat or prevent deep vein thrombosis (DVT), pulmonary embolism (PE), and stroke.

How is aPTT Test Performed?

The aPTT test is performed by drawing a small sample of blood, usually from a vein in the arm. The blood sample is then mixed with a reagent in a test tube, and the time it takes for the blood to form a clot is measured.

The results of the test are usually available within 30 to 60 minutes, and are expressed in seconds. The normal range for aPTT varies depending on the laboratory and the testing method used, but it is typically between 25 and 40 seconds.

Interpreting aPTT Test Results

An prolonged aPTT result may indicate a bleeding disorder or a problem with the clotting system. It can also occur as a side effect of certain medications, such as heparin or warfarin, or due to liver disease.

A decreased aPTT result may indicate an increased risk of blood clots, and may be seen in conditions such as disseminated intravascular coagulation (DIC) or factor IX deficiency (hemophilia B).

It is important to note that aPTT test results should be interpreted in conjunction with other clinical and laboratory data, and that a single abnormal result may not provide a definite diagnosis.


In conclusion, the aPTT test is a valuable tool for evaluating the function of the clotting system and for monitoring the effects of anticoagulant therapy. If you have questions or concerns about your aPTT test results, it is important to discuss them with your healthcare provider.


aPTT, Activated Partial Thromboplastin Time, blood clotting, bleeding disorders, anticoagulant therapy, warfarin, heparin, deep vein thrombosis, pulmonary embolism, stroke, clotting system, hemophilia, von Willebrand disease, test results, interpretation, healthcare provider.

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