Serum Antithrombin III Activity (Quantitative)
This test measures the level of antithrombin III, a natural protein in your blood that helps prevent blood clots from forming.
["Antithrombin III supports blood flow and reduces clot risk; low levels may indicate clotting disorders or liver issues."]
Key facts at a glance
- LOINC
- 29948-7
- Short code
- ENA SS-A Ab Titr Ser ID
- Synonyms
- ENA SS-A Ab Titr Ser ID
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- immune-diffusion
- 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 Might Be Ordered
Your doctor may recommend this test if you have a history of blood clots, unexplained bleeding, liver disease, or certain blood disorders. It can also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC).
What to Expect Before the Test
No special preparation is needed, but avoid smoking or consuming alcohol for 24 hours before testing. Fasted blood draws are common, but your doctor will guide you based on your specific situation.
How the Test Works
A small blood sample is drawn from a vein, usually in your arm. The sample is processed to measure antithrombin III activity using a specialized immunoassay method. This helps determine how effectively your blood can prevent clotting.
What the Results Mean
Results are reported as a percentage or ratio compared to a standard. Low levels may suggest conditions like antithrombin deficiency, liver disease, or certain medications affecting clotting. High levels may be normal or related to specific medical conditions.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Antithrombin III Activity
Frequently asked questions
Antithrombin III plays a critical role in regulating blood clotting. Low levels can increase the risk of clots, especially in people with inherited or acquired clotting disorders. It’s also important for monitoring patients on anticoagulant therapy to ensure safe blood thinning.
What causes low antithrombin III levels?
Your doctor will determine the frequency based on your health needs. If you have a clotting disorder or are on anticoagulant therapy, regular monitoring may be necessary. Follow your doctor’s instructions for follow-up testing.
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