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Activated Partial Thromboplastin Time

Also referred as

Partial thromboplastin time

Intrinsic pathway coagulation factor profile

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For men & women

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An Activated Partial Thromboplastin Time test is a screening test that helps evaluate your body's ability to form blood clots. This test is performed to detect bleeding disorders if you have unexplained bleeding or bruising and to monitor ongoing treatment with anticoagulant medicines.

Samples required

Blood

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Preparations

Overnight fasting required for 8 to 12 hours

Sample Collection

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Understanding Activated Partial Thromboplastin Time

Clotting factors or coagulation factors, are the proteins found in the blood that help to stop bleeding whenever there is a wound or cut. When any blood vessel is ruptured, the clotting factors initiate the formation of a blood clot that stops the bleeding rapidly. But when there is insufficient clotting factor in the blood, the blood clots do not form well, which leads to excessive bleeding.

An Activated Partial Thromboplastin Time (aPTT) also known as partial thromboplastin time (PTT) is performed to check if you have problems associated with your clotting factors which can result in excessive blood loss. This test helps diagnose various bleeding disorders, such as hemophilia, deep vein thrombosis (DVT), antiphospholipid syndrome, disseminated intravascular coagulation (DIC), etc. Your doctor may also suggest an Activated Partial Thromboplastin Time test if you have symptoms of bleeding or clotting disorders, such as unexplained and inappropriate heavy bleeding, easy bruising, unusual heavy nose bleeds, leg swelling, redness on the legs, or chest pain. Additionally, this test is performed in case of recurrent miscarriages and sometimes before a scheduled surgery.

Usually, overnight fasting (8-12 hours) is preferred before an Activated Partial Thromboplastin Time test, and a duly filled coagulation requisition form is mandatory for sample collection. If you take anticoagulant medication, it is advised to give the testing sample before the daily dose is taken. Also, inform the doctor if you are taking medications such as blood thinners, as they may interfere with test results, and your doctor may adjust your dose or stop them temporarily before the test.

Test result ranges are approximate and may differ slightly between different labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific test results. Narrate your as well as your family’s complete medical history of bleeding disorders to help the doctor correlate your clinical and laboratory findings. After analyzing all the aPTT test results, the doctor would recommend a course of treatment and lifestyle modifications such as diet and exercise to manage your condition.

What does Activated Partial Thromboplastin Time measure?

An Activated Partial Thromboplastin Time test measures the time taken by the blood to form a clot. In other words, it is a screening test that helps evaluate a person’s ability to form blood clots. The test analyzes the amount and the function of specific proteins in the blood called coagulation or clotting factors, which are an essential part of blood clot formation.

Blood clotting or coagulation occurs through a series of cascade reactions due to the activation of clotting factors. There are a total of thirteen clotting factors within our bodies that aid in clot formation, and for healthy clot formation, all clotting factors need to be in the right balance. Any imbalance of these factors can lead to a blood clotting disorder.

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FAQs related to Activated Partial Thromboplastin Time

Why is an Activated Partial Thromboplastin Time test important?

An Activated Partial Thromboplastin Time test is important in monitoring the treatment efficacy of blood-thinning medications, particularly heparin. An Activated Partial Thromboplastin Time test is also essential for diagnosing bleeding disorders or conditions that affect the clotting factors.

What are the risks associated with an Activated Partial Thromboplastin Time test?

Usually, there are no risks associated with an Activated Partial Thromboplastin Time test. However, some people may feel a slight sting when a needle is pricked and experience some bleeding that is normal and usually not bothersome. Rarely, some people may also experience slight swelling or bruising at the site of the needle prick. Applying ice 3-4 times a day for about a week may help reduce swelling and bruising. If it does not get better, consult your doctor.

When should I take an Activated Partial Thromboplastin Time test?

You may need an Activated Partial Thromboplastin Time test if you are experiencing symptoms suggestive of bleeding disorders, such as easily bleeding, unexplained heavy bleeding, heavy menstrual bleeding in women, excessive bleeding from cuts and wounds, frequent nosebleeds that won’t stop, bleeding gums, repeated heart attacks or strokes and excessive bleeding during surgical procedures.

What happens if my Activated Partial Thromboplastin Time test result is high?

If your Activated Partial Thromboplastin Time test result is higher than the normal range and you have certain symptoms associated with bleeding disorders like abnormal bleeding, easy bruising, etc., then it may indicate an underlying health problem like hemophilia, von Willebrand disease, liver disease, Vitamin K deficiency, etc. Talk to your doctor for a better understanding.

What factors can affect an Activated Partial Thromboplastin Time test result?

Certain medications like antihistamines, ascorbic acid, chlorpromazine, heparin, Vitamin K supplements, and salicylates may affect the test results. A high temperature can also alter an Activated Partial Thromboplastin Time test result.

Can I get an Activated Partial Thromboplastin Time test during pregnancy?

Yes, an Activated Partial Thromboplastin Time test may be done during pregnancy to determine any bleeding risks present in the patient, which can lead to miscarriage or thromboembolism.

What other tests can be advised by the doctor in case of abnormal results of an Activated Partial Thromboplastin Time test?

In case of abnormal results of an Activated Partial Thromboplastin Time test, the doctor can advise platelet count test, thrombin time test, fibrinogen testing, coagulation factor tests, lupus anticoagulant testing, and test for von Willebrand factor.

How can I control my unexplained bleeding that won’t stop?

Apply direct pressure on the cut or wound with a clean cloth, tissue, or a gauze piece until the bleeding stops. If blood soaks through, add another cloth or bandage and continue putting pressure on the cut. Seek medical help if the bleeding won’t stop.

Is there any difference between PTT and aPTT?

Both factors are used to calculate the time it takes the aPTT blood sample to clot in your body. However, in the case of aPTT (Activated Partial Thromboplastin Time), an activator (chemical agent) is added to the sample, speeding up the time it takes to clot. So, in aPTT, the reference range becomes narrower than in PTT (Partial Thromboplastin Time).

Content created by

Dr. Swati Gupta (Anand)

MBBS, MD Lab Medicine

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Last Updated

4th Nov 2025