What is aPTT?


What is aPTT? Understanding the Importance of Activated Partial Thromboplastin Time Test (aPTT)

When it comes to managing and treating blood clotting disorders, aPTT or activated partial thromboplastin time test is a crucial diagnostic tool. This test measures the time it takes for blood to clot, and it is used to identify any abnormalities in the clotting factors in a patient’s blood. In this article, we will cover everything you need to know about aPTT, including what it is, what it does, why it’s done, how it’s performed, its reference range, symptoms of high aPTT, low PTT, causes of aPTT low, and much more.

What is aPTT?

Activated partial thromboplastin time, commonly referred to as aPTT, is a medical test that measures the time it takes for blood to clot. The test evaluates the function of various clotting factors in the blood, including fibrinogen, prothrombin, and clotting factors VIII, IX, XI, and XII.

What Does the aPTT Test Do?

The aPTT test is used to diagnose and monitor blood clotting disorders, including hemophilia and von Willebrand disease. It is also used to monitor patients who are taking blood-thinning medications, such as heparin. By measuring the time it takes for blood to clot, aPTT can provide valuable information about the patient’s blood clotting ability and help doctors determine the best course of treatment.

Why is aPTT Test Done?

A doctor may order an aPTT test if a patient has symptoms of a bleeding or clotting disorder, such as easy bruising, unexplained nosebleeds, or heavy menstrual bleeding. The test may also be ordered before surgery or other procedures that could cause excessive bleeding. Additionally, patients who are taking anticoagulant medication may have their aPTT levels monitored to ensure that their medication is working correctly.

How is aPTT Test Performed?

To perform an aPTT test, a small sample of blood is drawn from the patient’s arm. The blood is then placed in a tube and mixed with a substance called a partial thromboplastin reagent. The reagent triggers the clotting process, and a timer is used to measure the time it takes for the blood to clot. The results of the test are typically available within a few hours.

What is aPTT Reference Range?

The reference range for aPTT varies depending on the laboratory performing the test. However, in general, a healthy person’s aPTT results fall between 25 and 35 seconds. If a patient’s aPTT is outside of the reference range, it may indicate a clotting or bleeding disorder.

What Are the Symptoms of aPTT Height?

A high aPTT result may indicate that the patient has a clotting disorder or is taking too much anticoagulant medication. Symptoms of a high aPTT result may include easy bruising, prolonged bleeding after injury or surgery, and heavy menstrual bleeding.

What is PTT Low?

PTT, or partial thromboplastin time, is another blood test that measures clotting time. If a patient’s PTT is low, it means that their blood is clotting more quickly than normal.

What Causes aPTT Low?

Several factors can cause a low aPTT result, including liver disease, vitamin K deficiency, or clotting factor deficiencies. In some cases, a low aPTT may also be due to anticoagulant medication, such as heparin.

How is aPTT Low Treated?

Treatment for low aPTT depends on the underlying cause of the condition. For example, if a patient has a vitamin K deficiency, they may be prescribed vitamin K supplements. If the low aPTT is due to liver disease, the underlying liver condition will need to be treated. If a patient is taking anticoagulant medication, their dosage may need to be adjusted.

What Are the Risks of aPTT Test?

Like any medical test, the aPTT test carries some risks. There is a small risk of infection, bleeding, or bruising at the site where the blood is drawn. However, these risks are relatively minor, and the benefits of the test generally outweigh the risks.

How to Prepare for an aPTT Test?

To prepare for an aPTT test, patients should inform their doctor of any medications they are taking, including over-the-counter medications, supplements, and herbal remedies. Some medications, such as anticoagulants, can affect the results of the test. Patients should also let their doctor know if they have any bleeding or clotting disorders, as this may affect the interpretation of the test results.


In summary, the aPTT test is a vital diagnostic tool used to evaluate the blood clotting ability of patients. By measuring the time it takes for blood to clot, doctors can identify and monitor blood clotting disorders, adjust the dosage of anticoagulant medications, and determine the best course of treatment for their patients. Understanding the importance of the aPTT test can help patients and healthcare providers work together to manage and treat blood clotting disorders effectively.


  1. What is the difference between aPTT and PT tests?

aPTT and PT tests are both blood tests used to evaluate blood clotting ability. The primary difference between the two tests is the clotting factors that they evaluate. aPTT measures the function of several clotting factors, including factors VIII, IX, XI, and XII, while PT measures the function of factors I, II, V, VII, and X.

  1. Can aPTT test detect blood clots?

No, aPTT testing is not used to detect blood clots. Instead, imaging tests such as ultrasound, CT scans, and MRI are used to diagnose blood clots.

  1. What is the difference between aPTT and INR tests?

aPTT and INR tests are both blood tests used to evaluate blood clotting ability. The primary difference between the two tests is the way the results are reported. aPTT results are reported in seconds, while INR results are reported as a ratio.

  1. Can aPTT test be done at home?

No, aPTT testing is not typically done at home. It is performed in a clinical laboratory by a trained healthcare professional.

  1. Can aPTT test be affected by stress?

No, stress does not typically affect the results of an aPTT test. However, stress can affect the results of other medical tests, so it’s important to inform your healthcare provider if you are experiencing stress or anxiety.

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