Antithrombin Activity Functional Test
Short Name: AT Activity Test
Also known as: Antithrombin III Activity Test, AT III Functional Assay, Antithrombin Functional Assay, AT Activity Chromogenic Test
Antithrombin Activity Functional Test test available at DNA Labs India for ₹4,000. Uses Chromogenic Assay on 3 mL whole blood in 1 Blue Top (Sodium Citrate) tube samples. Results in Same-day reporting for samples received by 11:00 AM. Reports are delivered via online portal, email, and WhatsApp.. Free home collection in 300+ cities across India.
🩺 Medically Reviewed By
Dr Pasupathy Arumugam
Consultant Pathologist · Reg: 21521
Last reviewed: September 7, 2026
Overview
The primary purpose of the Antithrombin Activity Functional Test is to detect and quantify deficiencies in antithrombin, a key natural anticoagulant protein. This test is used to diagnose hereditary or acquired antithrombin deficiency, evaluate patients with recurrent or unexplained venous thromboembolism (VTE), assess thrombophilia risk as part of a comprehensive clotting disorder workup, monitor antithrombin levels during heparin therapy (since heparin requires antithrombin to function), and investigate clotting tendencies in patients with a family history of thrombotic disorders.
- Test Code
- 165
- CPT Code
- 85300
- ICD Code
- D68.59
- Price
- ₹4,000
- Sample Type
- 3 mL whole blood in 1 Blue Top (Sodium Citrate) tube
- Result Time
- Same-day reporting for samples received by 11:00 AM. Reports are delivered via online portal, email, and WhatsApp.
- Fasting Required
- Yes (10 hours)
- Method
- Chromogenic Assay
Sample Collection
Overnight fasting is preferred. It is recommended that the patient, after consulting their physician, discontinues Heparin for 1 day and Oral anticoagulants (e.g., warfarin) for 7 days prior to sampling, as these drugs may affect test results. A duly filled Coagulation Requisition Form (Form 15) is mandatory.
Method: Venipuncture
Laboratory Analysis
A trained phlebotomist will collect 3 mL of venous blood using a standard venipuncture technique into a Blue Top (Sodium Citrate) tube. The tube must be mixed thoroughly by gentle inversion 8–10 times immediately after collection to ensure proper mixing with the anticoagulant.
Report Delivery
The sample must be transported to the laboratory within 4 hours at room temperature. If transport within 4 hours is not possible, prepare Platelet-Poor Plasma (PPP) within 1 hour of collection by centrifuging the sample at 3600 rpm for 15 minutes, transferring the supernatant to a clean plastic tube, centrifuging again at 3600 rpm for 15 minutes, and finally transferring the supernatant (PPP) to a labelled, clean plastic screw-capped vial. Freeze immediately. Ship frozen. Do not thaw.
Timeline: Same-day reporting for samples received by 11:00 AM. Reports are delivered via online portal, email, and WhatsApp.
Patient Instructions
About This Test
Who Should Get This Test
The primary purpose of the Antithrombin Activity Functional Test is to detect and quantify deficiencies in antithrombin, a key natural anticoagulant protein. This test is used to diagnose hereditary or acquired antithrombin deficiency, evaluate patients with recurrent or unexplained venous thromboembolism (VTE), assess thrombophilia risk as part of a comprehensive clotting disorder workup, monitor antithrombin levels during heparin therapy (since heparin requires antithrombin to function), and investigate clotting tendencies in patients with a family history of thrombotic disorders.
How to Prepare
- Use a Blue Top (Sodium Citrate) tube for blood collection.
- Collect exactly 3 mL of whole blood by venipuncture.
- Mix the tube thoroughly by gentle inversion 8–10 times immediately after collection.
- Transport the sample to the laboratory within 4 hours at room temperature (18–25°C).
- If transport is not possible within 4 hours, prepare Platelet-Poor Plasma (PPP) within 1 hour: centrifuge at 3600 rpm for 15 minutes, transfer supernatant to a clean plastic tube, centrifuge again at 3600 rpm for 15 minutes, and transfer final supernatant (PPP) to a labelled screw-capped vial.
- Freeze the PPP sample immediately and ship frozen. Do not thaw.
- A duly filled Coagulation Requisition Form (Form 15) is mandatory.
Doctor's Notes
Reviewed by Dr Pasupathy Arumugam — MBBS, MD (Pathology) · Reg. No. 21521
"Antithrombin deficiency is an underdiagnosed cause of recurrent venous thromboembolism. A functional antithrombin assay should be ordered when patients present with unexplained or recurrent blood clots, especially at a young age. I recommend this test as part of a comprehensive thrombophilia workup alongside Protein C, Protein S, and Factor V Leiden testing. Patients must inform their physician about any anticoagulant use prior to sample collection, as heparin and oral anticoagulants can interfere with results."
Last medically reviewed: September 7, 2026
Test Parameters & Specifications
Sample Stability
- Sample collected in incorrect tube (non-citrate tube)
- Sample not properly mixed by inversion
- Clotted or hemolyzed sample
- Insufficient sample volume (less than 3 mL)
- Sample received more than 4 hours after collection without PPP preparation
- Thawed frozen PPP sample
- Missing or incomplete Coagulation Requisition Form (Form 15)
Understanding Your Results
Antithrombin activity is within the normal reference range. No antithrombin deficiency detected. The body's natural anticoagulant mechanism is functioning adequately.
Status: Normal
Range: 80–120%
Mildly reduced antithrombin activity. This may be seen in heterozygous inherited deficiency, mild acquired deficiency, or may be influenced by acute illness, pregnancy, or estrogen therapy. Repeat testing and correlation with clinical findings is recommended.
Status: Mildly Decreased
Range: 60–79%
Moderately reduced antithrombin activity, significantly increasing the risk of venous thromboembolism. This level is commonly seen in heterozygous Type I or Type II antithrombin deficiency. Further investigation and specialist consultation are advised.
Status: Moderately Decreased
Range: 40–59%
Severely reduced antithrombin activity, associated with a very high risk of life-threatening blood clots. This may indicate homozygous antithrombin deficiency (rare and often fatal in infancy), severe acquired deficiency due to liver failure, DIC, or nephrotic syndrome. Urgent medical evaluation is required.
Status: Severely Decreased
Range: Below 40%
Elevated antithrombin activity is rarely clinically significant and is generally not associated with increased bleeding risk. It may occasionally be seen in patients on certain anticoagulant therapies. No specific action is usually required.
Status: Elevated
Range: Above 120%
Consult your doctor immediately if you have a family history of blood clots, have experienced recurrent deep vein thrombosis or pulmonary embolism, or develop symptoms such as sudden leg swelling, chest pain, shortness of breath, slurred speech, sudden vision loss, or weakness in the face, arm, or leg. If your test results show low antithrombin activity, seek specialist consultation with a haematologist for further evaluation and management.
Limitations
- ⚠This test measures functional activity only; it does not distinguish between Type I (quantitative) and Type II (qualitative) deficiency without additional antigen testing.
- ⚠Results may be affected by acute illness, inflammation, or concurrent anticoagulant therapy.
- ⚠A single low result should be confirmed with repeat testing before diagnosis.
- ⚠This test does not detect other causes of thrombophilia such as Factor V Leiden or Prothrombin gene mutation.
Risks & Considerations
- ●Minor bruising or discomfort at the venipuncture site
- ●Rare risk of slight bleeding in individuals with bleeding disorders
- ●Very rare risk of infection at the puncture site
Interfering Factors
- ●Heparin therapy – can falsely lower antithrombin activity results
- ●Oral anticoagulant therapy (e.g., warfarin) – may affect test interpretation
- ●Acute thrombosis or inflammatory conditions – may temporarily lower antithrombin levels
- ●Liver disease – can reduce antithrombin synthesis, leading to falsely low results
- ●Nephrotic syndrome – antithrombin loss through urine can reduce blood levels
- ●DIC (Disseminated Intravascular Coagulation) – consumes antithrombin, lowering levels
- ●Pregnancy – antithrombin levels may physiologically decrease during pregnancy
Compare With Similar Tests
| Test | Antithrombin Activity Functional Test | Antithrombin Antigen Test | Protein C Activity Test | Protein S Activity Test |
|---|---|---|---|---|
| Comparison | Antithrombin Activity Functional Test |
Frequently Asked Questions
What is the Antithrombin Activity Functional Test?
Why is the Antithrombin Activity Functional Test important?
What does a low antithrombin activity level indicate?
What is the cost of the Antithrombin Activity Functional Test in India?
Is fasting required before the Antithrombin Activity Functional Test?
What sample is required for this test?
What is the difference between the Antithrombin Activity Test and the Antithrombin Antigen Test?
Who should get the Antithrombin Activity Functional Test?
How long does it take to get the results?
Can I get home sample collection for this test?
Is the Antithrombin Activity Functional Test covered by insurance in India?
What are the symptoms of antithrombin deficiency?
Related Tests
Reference Laboratory Services
We serve as a reference laboratory for hospitals and clinics across India. Send samples from your facility with same-day pickup, priority processing, and results delivered through our online portal. Competitive institutional pricing available.
Your Data Privacy
Your medical data is protected under Indian law.
✓ Stored in India: All patient records are stored on servers located in India. No data is transferred outside the country.
✓ DPDP Act Compliant: Under the Digital Personal Data Protection Act 2023, you can request deletion of your records at any time by contacting support.
Book Your Test
Enter your details and we'll connect you within 15 minutes.