Antithrombin III (ATIII) Activity, Plasma
This test measures how well your blood naturally prevents blood clots from forming by checking levels of antithrombin III, a protein that helps regulate clotting. Low levels may suggest a higher risk of clotting disorders.
["Antithrombin III helps control blood clots; low levels may increase risk of clotting problems."]
Key facts at a glance
- LOINC
- 30985-6
- Short code
- Silver Birch (rBet v) 2 IgE Qn
- Synonyms
- Silver Birch (rBet v) 2 IgE Qn
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your doctor may order this test if you have a history of blood clots, certain blood disorders, or conditions that affect protein production in the liver. It can also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or to check for inherited clotting risks.
What to Expect Before the Test
No special preparation is needed. You may have a small needle inserted into a vein (usually in your arm) to draw blood. If you’re on blood thinners, let your doctor know before the test.
What the Results Mean
Results are typically reported as a percentage of normal activity. Very low levels (below 30%) may indicate a higher risk of clotting, while very high levels (above 150%) could suggest liver disease or other conditions affecting protein synthesis.
Common Conditions Linked to Results
Low antithrombin III levels are often seen in people with inherited clotting disorders (like antithrombin deficiency), severe liver disease, or conditions that cause widespread clotting (like DIC). High levels may be linked to liver disease or certain medications.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: Antithrombin III plays a critical role in preventing blood clots by inactivating clotting factors. Abnormal levels can signal underlying conditions that may require treatment, such as anticoagulant therapy or monitoring for inherited bleeding disorders.
Short name
Antithrombin III Activity
Frequently asked questions
What causes low antithrombin III levels?
How is antithrombin III tested?
Can antithrombin III levels change with diet?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy