Antithrombin III (ATIII) Mass Concentration in Plasma
This test measures the amount of antithrombin III, a natural protein in your blood that helps prevent blood clots from forming.
["Antithrombin III supports blood circulation by inhibiting clotting factors."]
Key facts at a glance
- LOINC
- 63169-7
- Short code
- ASPNIGG
- Synonyms
- A nidulans IgG-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top tube
- Units
- N/A
- Ref low
- 12
- Ref high
- 16
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Enzyme-linked immunosorbent assay (ELISA)
- CPT
- 86606
- SNOMED
- 122449009
- Specimen volume
- 1 mL serum (minimum 0.5 mL)
- Stability
- Stable for 7 days at 2-8°C; for longer storage, freeze at -20°C or below
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 48–120 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 are taking medications that increase your risk of clotting. It may also be checked before surgery or during treatment for conditions like disseminated intravascular coagulation (DIC).
What to Expect Before the Test
No special preparation is needed. You may have a small needle inserted into your arm or vein to draw a blood sample. If you’re on blood thinners, let your provider know beforehand to avoid unnecessary delays or complications.
What the Test Results Mean
Results are compared to a standard range for healthy adults. Low levels may indicate increased clotting risk, while very low levels could signal underlying conditions like liver disease or inherited disorders. Your provider will discuss results in the context of your health history.
Common Conditions Linked to Results
Low antithrombin III levels are often associated with conditions that increase clotting risk, such as thrombophilia (inherited or acquired), liver disease, or severe infections. High levels are less common but may occur in certain genetic conditions or during pregnancy.
Reference range
Negative: <12 mg/L; Equivocal: 12-16 mg/L; Positive: >16 mg/L (laboratory-specific)N/A
No special preparation required. Sample can be collected at any time of day.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Antithrombin III Level
Frequently asked questions
How often will I need this test?
What if my results are outside the normal range?
Can I eat or drink before this test?
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 15, 2026. · Read our editorial policy