Antithrombin Ill
Accurate Antithrombin III test to evaluate clotting function and thrombosis risk.
Turnaround time
3 business days
Biomarkers count
1
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Overview of the Antithrombin III Test
The Antithrombin III test is a specialist coagulation blood test that measures the activity of antithrombin, a naturally occurring anticoagulant protein that helps regulate blood clot formation. Antithrombin limits the activity of several clotting factors, particularly thrombin and factor Xa, helping prevent excessive or inappropriate clotting.
This is a single-biomarker coagulation test. It may be considered when investigating recurrent venous blood clots, a strong family history of thrombosis, suspected antithrombin deficiency or an unexpectedly reduced response to heparin. Antithrombin testing is also commonly considered alongside other thrombophilia markers such as Protein C, Protein S and Factor V Leiden.
Antithrombin activity can be affected by an active blood clot, anticoagulant treatment and certain medical conditions. A low result does not by itself confirm an inherited antithrombin deficiency, and results should be interpreted alongside medical history, medication use, previous clotting events and other relevant laboratory investigations.
What Does the Antithrombin III Test Check ?
This test measures 1 biomarker.
Antithrombin III activity
Measures the functional activity of antithrombin, a natural anticoagulant protein that helps regulate blood clotting by inhibiting several activated clotting factors. Reduced activity may be relevant when investigating an inherited or acquired tendency towards venous thrombosis, but results must be interpreted alongside clinical history, current treatment and other coagulation tests.
Who May Benefit From Antithrombin III Testing?
This test may be suitable for people who want to investigate antithrombin activity as part of an assessment of blood clotting, thrombosis risk or a previously abnormal coagulation result.
Investigate recurrent venous blood clots – Antithrombin activity may be assessed when someone has experienced more than one unexplained venous thrombosis.
Explore a previous deep vein thrombosis – Testing may form part of a wider thrombophilia assessment after an unexplained DVT.
Investigate a previous pulmonary embolism – Antithrombin may be considered alongside other clotting markers where a PE has occurred without an obvious explanation.
Review a family history of thrombosis – Testing may provide useful information where close relatives have confirmed antithrombin deficiency or significant venous clotting histories.
Investigate blood clots occurring at a younger age – Unexplained thrombosis at a relatively young age may prompt investigation of inherited clotting factors.
Assess unusual or recurrent clotting patterns – Antithrombin activity can be included within specialist investigations where clotting occurs repeatedly or in an unusual clinical context.
Investigate reduced response to heparin – Antithrombin is required for heparin's anticoagulant effect, so testing may sometimes be relevant where unusually high doses are required.
Follow up a previous low antithrombin result – Repeat testing may be recommended once temporary factors that could influence the result have resolved.
Arrange a private blood test in London – Access specialist coagulation testing through London Blood Tests without relying solely on routine GP referral pathways.
How to Prepare
Do not stop heparin, warfarin, DOACs or any other prescribed anticoagulant specifically for this test unless the clinician responsible for your treatment tells you to do so. If you are currently taking anticoagulants or have recently experienced a blood clot, discuss the timing of testing before collection.
Symptoms and Reasons to Consider the Antithrombin III Test
You may wish to consider the Antithrombin III test if you have a personal or family history that raises questions about abnormal blood clotting. Antithrombin deficiency itself may not cause day-to-day symptoms unless a clot develops, so medical history is often more relevant than general symptoms.
Previous deep vein thrombosis (DVT) – A history of an unexplained clot in a deep vein may prompt thrombophilia investigation once the acute event has resolved.
Previous pulmonary embolism (PE) – Antithrombin testing may be considered as part of a broader assessment after an unexplained venous clot travels to the lungs.
Repeated episodes of venous thrombosis – Recurrent blood clots may warrant assessment of natural anticoagulant proteins.
Blood clot at a relatively young age – Early venous thrombosis may be one reason a clinician considers inherited thrombophilia testing.
Blood clot without a clear trigger – Testing may be relevant where thrombosis occurs without recent surgery, prolonged immobility or another obvious provoking factor.
Blood clot in an unusual location – Specialist assessment may be appropriate when thrombosis occurs outside the more typical veins of the legs or lungs.
Close relative with antithrombin deficiency – Family testing may be considered where an inherited deficiency has already been identified.
Strong family history of unexplained blood clots – Multiple affected relatives may justify discussion of specialist coagulation testing.
Unexpected difficulty achieving anticoagulation with heparin – Reduced antithrombin activity can be relevant because heparin relies on antithrombin for much of its anticoagulant effect.
Previous abnormal thrombophilia results – Antithrombin activity may be repeated or reviewed alongside Protein C, Protein S and genetic clotting investigations.
Antithrombin is one of the body's natural mechanisms for limiting excessive clot formation. Reduced activity can be inherited, but temporary or acquired reductions can also occur, which is why a single low result should not automatically be interpreted as a hereditary disorder.
Blood clot symptoms require medical assessment rather than relying on private testing. New one-sided leg swelling or pain, sudden unexplained breathlessness, chest pain, coughing blood or collapse can indicate a potentially serious clot and require urgent medical attention. Antithrombin results should be interpreted alongside symptoms, medical history, medications, the timing of any previous thrombosis and professional clinical advice.
How to Book Your Antithrombin III Test in London
Booking your Antithrombin III test with London Blood Tests is simple and designed to fit around your schedule.
Choose the Antithrombin III
Select the Antithrombin III test online and review the test information before booking.
Select your sample collection option
Choose an in-clinic blood draw (+£35) or a home or hotel phlebotomy visit (+£60) where a qualified phlebotomist collects your sample.
Attend your appointment
A trained professional will collect your blood sample safely and efficiently at the clinic or during your arranged home or hotel visit.
Laboratory analysis
Your sample is sent to the laboratory, where Antithrombin III activity is analysed to assess the functional activity of this natural anticoagulant protein.
Receive your results securely
Your results are sent securely by email, ready to review yourself or discuss with a GP, haematologist, specialist or qualified clinician.
When Will I Receive My Results?
The expected turnaround time for the Antithrombin III test is approximately 3 business days.
Your results are sent securely by email once laboratory analysis and authorisation are complete. Turnaround normally begins when the laboratory receives your sample rather than necessarily from the date your blood is collected.
Coagulation testing can occasionally require repeat analysis or further laboratory review, which may extend the expected turnaround. Results outside the laboratory reference range should be discussed with a GP, haematologist or suitably qualified clinician.
Understanding Your Results
Your Antithrombin III report will show the measured antithrombin activity together with the reference range used by the analysing laboratory. Reference ranges can vary between laboratories and analytical methods, so your result should be interpreted using the range supplied on your own report.
A low Antithrombin III activity result may be seen with inherited antithrombin deficiency, but it can also occur temporarily or as a result of other clinical circumstances. Active thrombosis, heparin treatment, liver disease, certain kidney conditions and other acquired factors may affect antithrombin levels.
A normal result does not exclude all inherited or acquired thrombophilias, while a low result does not automatically confirm hereditary antithrombin deficiency. If activity is reduced, repeat testing or additional investigations such as antithrombin antigen testing may sometimes be considered to help determine whether the finding is persistent and whether the amount or function of antithrombin is affected.
Results should be interpreted alongside age, personal and family history of thrombosis, current and recent anticoagulant medication, previous blood clots and other thrombophilia investigations.
Why Book With London Blood Tests?
Private blood testing in London – Access specialist Antithrombin III activity testing through London Blood Tests.
Clinic and home visit options – Choose an in-clinic blood draw or request home or hotel phlebotomy depending on location and availability.
Specialist coagulation testing – Access individual clotting tests alongside wider thrombophilia and haematology investigations.
Secure results by email – Receive your authorised laboratory report securely once analysis is complete.
Clear pricing before booking – The Antithrombin III test is priced at £99, with sample collection charges shown separately.
Convenient appointment process – Arrange private sample collection around your schedule.
Support with choosing the right test – London Blood Tests can help if you are unsure which coagulation or thrombophilia investigation has been requested.
Private testing without a long wait – Access specialist laboratory testing without relying solely on routine referral pathways.
Private Antithrombin III Blood Test in London
London Blood Tests provides private Antithrombin III blood testing in London for people who want to assess antithrombin activity following a previous clotting event, family history, abnormal coagulation result or recommendation from a healthcare professional.
Clinic appointments are available alongside home and hotel phlebotomy depending on location and availability. Flexible sample collection makes it easier to arrange a private blood test near me while maintaining a discreet and convenient testing process.
Antithrombin activity provides focused laboratory information about one part of the body's natural anticoagulant system. It is often most useful when interpreted alongside other thrombophilia tests and clinical history, particularly by a GP, haematologist or another healthcare professional familiar with your clotting history.