Antithrombin III Antigen Test
About Antithrombin III Antigen Test
| Field | Value |
|---|---|
| Also Known As | AT III, AT 3, Functional Antithrombin, Heparin Cofactor I, AT Antigen, Antithrombin III Immunologic, Deep Vein Thrombosis - AT III test. |
| Sample Type | Venous blood (citrated plasma) |
| Fasting Required | No fasting needed |
| Report Time | 8 to 12 working days |
| Recommended For | Adults and children of all genders, especially those with clotting disorders or a family history of thrombosis |
| Price | Starting at ₹1,550 |
What Is an Antithrombin III Antigen Test?
The Antithrombin III antigen test measures the amount of antithrombin protein present in the blood. Antithrombin is a protein that controls blood clotting by blocking certain clotting factors. Doctors order this test when they suspect a clotting disorder or when a patient does not respond as expected to blood-thinning treatment. A venous blood sample, drawn from the arm, is used for this test.
What Does an Antithrombin III Antigen Test Measure?
The AT III test evaluates a plasma glycoprotein, a protein with sugar molecules attached, that plays a key role in preventing excessive blood clot formation. There are two main types of antithrombin tests. The functional assay (activity test) checks whether the protein is working correctly. If activity is low, the antithrombin antigen assay is then done to find out whether there is too little protein (Type I deficiency) or a dysfunctional protein (Type II deficiency). The following table summarises the parameters measured:
| Parameter | What It Indicates |
|---|---|
| AT III Antigen Level | The quantity of antithrombin protein present in the blood |
| Type I vs Type II Distinction | Whether the deficiency is due to reduced quantity or abnormal protein function |
Why Is an Antithrombin III Antigen Test Done?
This test helps doctors investigate unexplained clotting problems and assess antithrombin deficiency. Below are the common reasons a doctor may order it.
Common Symptoms That May Require This Test
The following symptoms may prompt a doctor to order an AT III test:
- Unexplained or recurrent blood clots
- Headaches
- Seizures
- Shortness of breath without a clear cause
- Chest pain related to a possible clot
- Poor or unexpected response to heparin (a blood-thinning medicine)
- Preeclampsia
- Repeated miscarriages
- Known family history of antiphospholipid
Conditions This Test Can Help Detect
The antithrombin antigen test can help identify several conditions, including:
- Hereditary antithrombin deficiency, which may cause blood clots in veins from a young age
- Deep vein thrombosis (DVT), a blood clot forming in a deep vein, often in the leg
- Pulmonary embolism, a clot that travels to the lungs
- Liver cirrhosis or liver failure, which reduces antithrombin production
- Nephrotic syndrome, a kidney disorder causing protein loss in the urine
- Disseminated intravascular coagulation (DIC), a serious disorder affecting the clotting system
- Certain cancers and protein-losing gut conditions
Antithrombin III Antigen Test for Chronic Disease Monitoring
For patients with known antithrombin deficiency, this test is used to monitor how well antithrombin replacement therapy is working. Those who have had clotting events or are at high risk may need more regular testing, particularly during anticoagulant treatment. Your doctor will decide the appropriate testing frequency based on your individual medical history.
How to Prepare and What to Expect
Preparing for this test is straightforward. Here is what you need to know before your appointment.
Do You Need to Fast?
No fasting is required before an antithrombin III antigen test. However, if your doctor has ordered additional tests alongside this one, some of those may require fasting, so confirm with your doctor in advance.
Practical Tips Before Your Test
Keep the following points in mind before getting tested:
- Tell your doctor about all medications you are currently taking, especially blood thinners such as warfarin, heparin, or dabigatran
- Avoid testing while on unfractionated heparin therapy, as it can lower antithrombin activity levels
- Ideally, schedule the test at least a couple of months after a clotting episode
- Wait at least six weeks after stopping anticoagulant medicines before testing, unless your doctor advises otherwise
- Stay well hydrated on the day of the test
Step-by-Step Procedure
The sample collection process is quick and simple. Here is what to expect:
- You will be seated with your arm resting on a support. A tourniquet (a soft band) is placed around your upper arm to make the vein easier to locate.
- The skin over the vein is cleaned with an antiseptic solution to prevent infection.
- A sterile, disposable needle is gently inserted into the vein. Blood is drawn into a labelled blue-top tube containing a special anticoagulant (sodium citrate) to preserve the sample.
- Once sufficient blood is collected, the tourniquet is removed. The needle is withdrawn, and light pressure is applied to the site.
- A small bandage is placed on the puncture site. The entire procedure usually takes no longer than five minutes.
Factors That Can Affect Accuracy
Certain factors may influence the reliability of your results. These include:
- High levels of haemoglobin, bilirubin, or triglycerides in the blood sample
- Use of thrombin inhibitors, which can overestimate antithrombin levels in some assay types
- A clotted, haemolysed (broken red blood cells), or incorrectly filled sample tube
- Lipemia (elevated fats in the blood), jaundice, or improper sample storage
Understanding Your Antithrombin III Antigen Test Results
Results from this test should always be reviewed alongside your full medical history. A doctor is best placed to explain what your numbers mean for your individual situation. The reference ranges below are general guidelines used by most laboratories.
| Parameter | Reference Range |
|---|---|
| AT III (Newborns) | 44% to 76% |
| AT III (Adults) | 80% to 120% |
These ranges are general guidelines. Your doctor will interpret your results based on your age, health history, and other factors. Always consult a qualified healthcare professional for personalised medical advice.
Results During Special Conditions
Certain situations can affect your antithrombin antigen plasma levels. Your doctor will take these into account when reading your results.
- Pregnancy naturally lowers AT III levels by around 20% compared to baseline. Levels drop further as pregnancy progresses and fall sharply immediately after delivery.
- Treatment with unfractionated heparin can reduce AT III levels by up to 30%, which may result in a falsely low reading during the treatment period.
- Oral anticoagulants such as warfarin can raise AT levels, potentially masking a deficiency in people with a heterozygous (partial) hereditary deficiency.
- Oestrogen-containing contraceptives and asparaginase-based chemotherapy may also lower antithrombin antigen levels.
How to Maintain Healthy Levels
While antithrombin levels are largely determined by genetics and underlying health conditions, the following general wellness steps support good circulatory health:
- Maintain a healthy weight and stay physically active to promote good blood flow
- Avoid smoking and limit alcohol, as both can affect liver function — the liver produces antithrombin
- Speak to your doctor before starting any hormonal therapy, including oral contraceptives, as these can influence antithrombin activity
Lupin Diagnostics Antithrombin III Antigen Test Price and Home Collection
The antithrombin III antigen test is available at a starting price of ₹1,550, with home sample collection available across major Indian cities. The table below shows approximate prices by city, sourced from aggregator data.
| City | Approximate Price (₹) |
|---|---|
| Guwahati | ₹1,550 |
| Mumbai | ₹1,550 |
| Bangalore | ₹1,550 |
| Chennai | ₹1,550 |
| Hyderabad | ₹1,550 |
| Kolkata | ₹1,550 |
| Pune | ₹1,550 |
| Bhubaneshwar | ₹1,550 |
Prices are indicative and may vary by location. Please confirm the current price at the time of booking.
How to Book
- Select the test on the Lupin Diagnostics website.
- Choose your city and preferred time slot.
- Opt for home sample collection by a certified phlebotomist, or visit your nearest Lupin Diagnostics centre.
- Receive your report via email or WhatsApp within the stipulated turnaround time.
Home Collection
Lupin Diagnostics offers home sample collection across cities, so you do not need to visit a centre unless you prefer to. All samples are processed in NABL-accredited laboratories by trained staff. Your digital report is delivered directly to your email or WhatsApp once ready.
Frequently Asked Questions
The activity (functional) test checks whether the antithrombin protein is working properly, and is usually done first. If activity levels are low, the antigen test is then ordered to find out whether there is less protein than normal (Type I deficiency) or whether the protein is present but not functioning correctly (Type II deficiency).
Testing while on unfractionated heparin is generally not recommended, as heparin can lower AT III levels and give a falsely low result. It is also advisable to wait at least six weeks after stopping anticoagulants before testing.
Your doctor may order this test if you have had repeated or unexplained blood clots, if heparin treatment is not producing the expected effect, or as part of a broader investigation into clotting disorders. It is also used to monitor treatment in people already diagnosed with antithrombin deficiency.
Hereditary antithrombin deficiency is a rare condition passed on in an autosomal dominant pattern, meaning one copy of the altered gene from either parent is enough to cause the condition.
Yes. Antithrombin levels naturally fall during pregnancy by around 20% compared to pre-pregnancy levels, and drop further after delivery. Women with known antithrombin deficiency face a higher risk of blood clots during pregnancy. This is managed under close medical supervision and is not part of routine prenatal screening.
Yes, several medicines can interfere with results. Warfarin may raise AT levels, potentially making a deficiency appear less severe. Thrombin inhibitors such as dabigatran, hirudin, and argatroban can interfere with certain laboratory assay methods. Always give your doctor a full list of your current medications before testing.
No fasting is required. However, do inform your doctor about any medicines or supplements you are taking, as some can affect your results.
Antithrombin III Antigen Test
