Also called: AT test, AT3, Antithrombin III test
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The Anti-Thrombin III test measures the level of antithrombin, a natural protein that helps regulate blood clotting by preventing excessive clot formation. Deficiency of antithrombin increases the risk of abnormal blood clots in veins and arteries.
This test is crucial in evaluating inherited or acquired clotting disorders, especially in patients with unexplained or recurrent thrombosis.
You may be advised this test to:
Evaluate recurrent or unexplained blood clots
Investigate thrombosis occurring at a young age
Assess pregnancy-related clotting complications
Screen for inherited clotting disorders
Evaluate family history of thrombosis
Antithrombin is a natural anticoagulant protein produced by the liver. It works by inactivating several clotting factors, preventing excessive clot formation. When antithrombin levels are low, the balance shifts toward clot formation, significantly increasing thrombosis risk. This test helps identify both inherited deficiencies (present from birth) and acquired deficiencies (developing due to other conditions).
Recurrent deep vein thrombosis (DVT)
Pulmonary embolism
Blood clots at unusual sites
Thrombosis at a young age (under 50)
Pregnancy-related clotting events
Family history of clotting disorders
Unexplained clot formation
Early detection of antithrombin deficiency helps prevent life-threatening clot formation and allows timely initiation of anticoagulant therapy. It also helps guide treatment decisions and family screening.
Inform your doctor about all medications, especially anticoagulants
Testing is ideally done when not on blood thinners, as they can affect results
No fasting is typically required
Discuss timing with your doctor if you're pregnant or recently had surgery
A blood sample is drawn from a vein in your arm and sent to the laboratory for analysis using specialized immunoassay or functional activity testing methods.
Results are typically available within a few days. If levels are low, your doctor may recommend repeat testing to confirm the diagnosis and rule out temporary causes.
Immediately if you experience symptoms of blood clots such as leg pain and swelling, chest pain, shortness of breath, or if your test results show low antithrombin levels.
Minimal risk related to blood draw only, including slight bruising or discomfort at the puncture site.
Stay active and avoid prolonged immobility
Maintain adequate hydration
Follow prescribed anticoagulant therapy if recommended
Inform healthcare providers about your condition before surgery
Wear compression stockings during long travel if advised
Avoid smoking, which increases clot risk
The test measures the concentration and functional activity of antithrombin III, a key anticoagulant protein that regulates blood clot formation.
Normal levels (80–120%): Antithrombin deficiency unlikely
Low levels (<80%): Increased risk of abnormal blood clots; may indicate inherited or acquired deficiency
Borderline levels: May require repeat testing for confirmation
Seek specialist care (hematologist) for further evaluation, confirmatory testing, family screening, and discussion of long-term anticoagulation therapy if needed.
Current use of anticoagulants (heparin, warfarin)
Acute thrombosis or recent clot formation
Liver disease
Pregnancy
Recent surgery or trauma
Certain medications
Timing of sample collection
Is antithrombin deficiency common?
No, antithrombin deficiency is rare, occurring in approximately 1 in 2,000 to 5,000 people, though it accounts for a significant proportion of inherited clotting disorders in younger patients with unexplained thrombosis.
Is it inherited?
Yes, antithrombin deficiency is often inherited in an autosomal dominant pattern, meaning a child has a 50% chance of inheriting the condition if one parent carries the deficiency; however, acquired deficiency can also occur.
Can pregnancy affect levels?
Yes, pregnancy can lower antithrombin levels temporarily due to increased consumption, hemodilution, and hormonal changes, which increases clotting risk; testing may need careful interpretation during pregnancy and postpartum periods.
Is treatment lifelong?
Sometimes, treatment duration depends on whether the deficiency is inherited or acquired, and whether clots have occurred; those with inherited deficiency and recurrent clots typically require lifelong anticoagulation therapy.
Is repeat testing required?
Yes, repeat testing is usually required to confirm the diagnosis, especially if initial levels are borderline or if testing was done during acute illness, anticoagulant use, or pregnancy when results may be temporarily affected.
Antithrombin III is a natural protein that stops your blood from clotting too much. This test is advised if:
Tapadia Diagnostic Centre in Aurangabad offers NABL-accredited Antithrombin III test from a Blood sample(s). AT test, AT3, Antithrombin III test is also prescribed for Chest pain, leg swelling, breathing trouble. Established in 1989, this doctor-led diagnostic centre ensures high accuracy. Home sample collection and walk-in facility available at our Aurangabad center. Pay at the centre with no advance payment. Book online or visit us.
Antithrombin III in Aurangabad
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