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Activated Partial Thromboplastin Time (aPTT) Test

Also known as  PTT test | APTT - TEST | Activated Partial Thromboplastin Time (aPTT) | Activated Partial Thromboplastin Time (aPTT)
The aPTT is one of several blood coagulation tests. It measures how long it takes your blood to form a clot. Normally, when blood vessels are damaged, proteins in the blood are called clotting factors, and they come together in a certain order to form blood clots and quickly stop bleeding.
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What is the activated partial thromboplastin time (aPTT) test? 

Activated Partial Thromboplastin Time (aPTT), also called partial thromboplastin time (PTT), is a screening test that helps evaluate a person’s ability to form blood clots appropriately.

This test is done to detect bleeding and clotting disorders and to monitor the treatment with blood-thinning medicines. In cases of unexplained bleeding, inappropriate blood clotting, or recurrent miscarriages, and sometimes before a scheduled surgery, an aPTT test is performed. These tests are usually performed with other tests like prothrombin time and thrombin time to analyze the clotting time accurately.

If the values were higher than normal, it could be due to a bleeding disorder or liver disease. If the values are lower than normal, they can indicate that you may have a chance of getting blood clots and several miscarriages.

What are the other names for the activated partial thromboplastin time (aPTT) test? 

Other names are aPTT and PTT test.

What parameters are included in an activated partial thromboplastin time (aPTT) test?

There is only one parameter.

What does the activated partial thromboplastin time (aPTT) test measure?

This test measures the time taken by the blood to form a clot after the addition of substances (reagents) that activate the clot formation.

In the event of any bleeding, the body responds by forming a blood clot as quickly as possible. This process of blood clotting or coagulation is called hemostasis, and it involves a series of chemical reactions in the blood (coagulation cascade). During this process, the blood proteins called factors are activated one after another in a series. These activated coagulation factors lead to the formation of fibrin mesh around the platelets and other blood cells at the site of bleeding, and this complex hardens to form a “blood clot."

The coagulation cascade proceeds through two pathways: the intrinsic pathway and the extrinsic pathway. These pathways will later be merged together into a common pathway. The Activated Partial Thromboplastin Time (aPTT) test measures the function of blood coagulation factors I, II, V,XII, VIII, IX, X, and XI, along with other factors like Prekallikrein (PK), and High Molecular Weight Kininogen (HK), that form parts of the intrinsic and common coagulation pathways.

This aPTT test result is compared to a control sample of normal blood.

The aPTT test is usually performed along with a Prothrombin Time (PT)test to evaluate the cause of a coagulation defect, if any. 

What’s the normal range of the activated partial thromboplastin time (aPTT) test?

21 to 35 seconds.

Who should get an activated partial thromboplastin time (aPTT) test? 

The PTT may be recommended along with other tests, such as a PT when you have:

  1. Unexplained bleeding or easy bruising.
  2. Blood clots in a vein or an artery.
  3. This acute condition, such as disseminated intravascular coagulation(DIC), might cause both bleeding and clotting as a coagulation factor is used up at a rapid rate.
  4. A chronic condition such as liver disease may affect clotting.

A PTT may be ordered.

  1. as part of an evaluation for lupus anticoagulant (LA),anticardiolipin antibodies (ACA), and antiphospholipid syndrome, when you have had a blood clot or when a woman has had recurrent miscarriages.
  2. When you are switched from heparin therapy to longer-term warfarin(Coumadin®) therapy, the two are overlapped and both the PTT and PT are monitored until you have stabilized.
  3. When you have a surgical operation scheduled, you may have ordered aPTT prior to surgery when the surgery carries an increased risk of blood loss and/or when you have any clinical history of bleeding, such as frequent or excessive nose bleeds and easy bruising, which may indicate the presence of a bleeding disorder.

Are preparations needed for the activated partial thromboplastin time (aPTT) test?

Fasting is not required for this test.

What is the cost of a aPTT test?

APTT Test in Bangalore₹ 420
APTT Test in Delhi₹ 480
APTT Test in Gurgaon₹ 450
APTT Test in Noida₹ 450
APTT Test in Hyderabad₹ 550

What is the type of sample required? 

This test requires a blood sample.

Who will process the activated partial thromboplastin time (aPTT) test?

A healthcare provider, who is also called a phlebotomist, usually performs blood draws, including those for an Activated Partial Thromboplastin Time (aPTT) test, but any healthcare provider trained in drawing blood can perform this task. The samples are sent to a lab where a medical laboratory scientist prepares the samples and performs the tests on analyses or manually.

What should I expect during my activated partial thromboplastin time (aPTT) test?

You may expect to experience the following during the blood test or blood draw:

  1. You have to sit comfortably on the chair, and a healthcare provider will check your arms for an easily accessible vein. This is the inner part of your arm on the other side of your elbow.
  2. Once they have located a vein, they will disinfect the area with an alcohol swab.
  3. They will insert a small needle into the vein to draw a blood sample. This can feel like a small pinch.
  4. After the needle is inserted, the required amount of blood will be collected in a test tube.
  5. When they've collected enough blood for the test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop any bleeding.
  6. They will apply a band-aid over the pricked site, and the blood collection is finished.

This process takes less than five minutes.

What should I expect after my activated partial thromboplastin time (aPTT) test?

Once the phlebotomist has collected the blood sample, it will be sent to the laboratory for processing or testing. When the reports are ready, your healthcare provider will share the results with you.

What is the risk of the activated partial thromboplastin time (aPTT) test?

These blood tests are common and don’t carry any significant risks. You might have a slight pain like an ant bite when the needle gets pricked, and a small bruise can develop there.

When can I expect my activated partial thromboplastin time (aPTT) test results?

Orange Health reports are available via email or WhatsApp within 6 hours of the collection of the blood sample.

What do the results of an activated partial thromboplastin time (aPTT) test mean?


PTT results are typically reported in seconds.

The aPTT result that falls within a laboratory’s reference interval usually indicates normal clotting function. However even with a normal PTT result, mild to moderate deficiencies of a single coagulation factor might be present. The PTT might not be prolonged until the factor levels have decreased to 30% to 40% of normal. On the other hand, a lupus anticoagulant may be present but may not prolong the PTT result. If the lupus anticoagulant (LA) is suspected, a more sensitive LA-sensitive PTT or a dilute of the Russell viper venom time (DRVVT) can be used to test for it. (Check below for more about LA-sensitive PTT.)

Prolonged PTT means that the clotting is taking much longer to occur than normal and may be due to a variety of causes.

A prolonged PTT may be due to:

The underlying conditions that cause low levels of clotting factors, such as:

  1. Liver disease - Most coagulation factors are produced by the liver, so liver disease may cause prolonged PT and PTT. However, the PT is more likely to be prolonged than the PTT.
  2. Vitamin K deficiency - Vitamin K is very essential for the formation of several clotting factors. These Vitamin K Deficiencies are rare, but they can be caused by an extremely poor diet, malabsorption disorders, or prolonged use of certain antibiotics, for example. PT values are more likely to be prolonged than PTT.

Less common inherited clotting factor deficiencies:

  1. Von Willebrand disease (vWD) is the most commonly inherited bleeding disorder, and it affects platelet function due to decreased Von Willebrand factor. PTT is normal in most cases of vWD but can be prolonged in severe vWD.
  2. Hemophilia A and hemophilia B (Christmas disease) are two other types of inherited bleeding disorders resulting from a decrease in the factors VIII and IX, respectively.
  3. Deficiencies of other coagulation factors, like factors XII and XI, A deficiency in XI can cause abnormal bleeding, but the deficiency in XII is not associated with bleeding risk in the body.

A nonspecific inhibitor such as the lupus anticoagulant is an autoantibody (antiphospholipid antibody) that interferes with the PTT because it targets substances called phospholipids that are used in the PTT. In addition, they can have a prolonged PTT result in the body because they are associated with excessive clotting.

A person who produces these antibodies may be at an increased risk of blood clots.

  1. A specific inhibitor - Although relatively rare, these are antibodies that specifically target certain coagulation factors (known as factor-specific inhibitors), affecting how they function. An example is an antibody that targets factor VIII. Factor-specific inhibitors can cause severe bleeding.
  2. This heparin is an anticoagulant and will prolong a PTT, either because it may contaminate the sample or as part of anticoagulation therapy. For this anticoagulant therapy, the target value of PTT is often about 1.5 to 2.5 times longer than a person’s pre - treatment level. PTT is still being used as a monitor for standard heparin therapy.
  3. Warfarin (Coumadin®) anticoagulation therapy - the PTT is not used to monitor warfarin therapy, but the PTT may be prolonged by warfarin at a high dose. This is typical, the prothrombin time/international normalized ratio (PT/INR) is used to monitor warfarin therapy.
  4. Other anticoagulants - anticoagulation therapy with direct thrombin inhibitors (e.g., argatroban, dabigatran) or direct factor Xainhibitors (e.g., rivaroxaban, apixaban).
  5. These prolonged PTT levels can also be seen with certain types of leukemia, excessive bleeding in pregnant women prior to or after giving birth, or recurrent miscarriages.

These results of the PTT are often interpreted with the results of the PT in determining what condition may be present.​

What is the normal range for the activated partial thromboplastin time (aPTT) test results? 

The normal range of the activated partial thromboplastin time (aPTT) test results is 21 - 35 seconds. Normal ranges can vary slightly among the different laboratories. Some labs use different measurements or may test with different samples. Talk with the doctor about the meaning of your specific test results.

What other tests might I have along with this test?

APLA, Lupus Anticoagulant, and Cardiolipin

How do I book an aPTT test at home?

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