Serum Antithrombin III Concentration (Mass Concentration)
This test measures the amount of antithrombin III, a natural protein in your blood that helps prevent abnormal blood clots from forming.
["Antithrombin III plays a key role in blood clotting regulation; low levels may increase your risk of clotting disorders."]
Key facts at a glance
- LOINC
- 31625-7
- Short code
- ENA SS-A IgG Ser Ql
- Synonyms
- ENA SS-A IgG Ser Ql
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 82784
- 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 healthcare provider may recommend this test if you have a history of blood clots, certain blood disorders, or if you’re taking medications that affect blood clotting, such as anticoagulants. It may also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or inherited clotting disorders.
What to Expect Before the Test
No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your blood is drawn early in the morning. Wear a loose shirt for easy access to your arm.
How the Test Is Performed
A healthcare professional will insert a needle into a vein in your arm to draw a blood sample. You may feel a slight pinch, but the procedure is quick. The blood is then sent to a lab for analysis.
What the Results Mean
Results are reported as a concentration value (e.g., grams per deciliter). Low levels of antithrombin III may indicate an increased risk of clotting, while normal or high levels suggest healthy blood clotting regulation. Your provider will interpret results in the context of your medical history.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Antithrombin III (ATIII) Level
Frequently asked questions
What does a low antithrombin III level mean?
Antithrombin III is unique because it directly inhibits enzymes involved in blood clot formation. Unlike other clotting factors (such as prothrombin or fibrinogen), it acts as a natural anticoagulant. Your provider may compare this test with others, like prothrombin time (PT) or activated partial thromboplastin time (aPTT), depending on your symptoms.
Dietary factors generally do not significantly affect antithrombin III levels. However, certain medications (like anticoagulants) or medical conditions (such as liver disease) can influence it. If you’re taking supplements or have dietary restrictions, let your provider know to ensure accurate results.
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