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Serum Antithrombin III Concentration (Mass Concentration)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of antithrombin III, a natural protein in your blood that helps prevent blood clots from forming. Low levels may increase your risk of clotting problems.

Quick summary

["Antithrombin III helps regulate blood clotting; low levels may signal clotting disorders or other health risks."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
33569-5
Short code
ENA SS-A Ab Ser IA-aCnc
Synonyms
ENA SS-A Ab Ser IA-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
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 healthcare provider 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 might also be checked before surgery, during pregnancy, or if you’re taking medications that increase clotting risk.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm to draw blood. If you’re on blood thinners, let your provider know beforehand.

What the Results Mean

Results are compared to a standard range for healthy adults. Very low levels may indicate conditions like liver disease, disseminated intravascular coagulation (DIC), or inherited clotting disorders. Very high levels are less common but could suggest certain genetic or inflammatory conditions.

Common Conditions Affecting Results

Low levels of antithrombin III can be linked to inherited deficiencies (e.g., antithrombin III deficiency), liver disease, or conditions like sepsis or pregnancy. High levels may rarely be seen in conditions like nephrotic syndrome or certain infections.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Antithrombin III (ATIII) Level

Frequently asked questions

What causes my antithrombin III level to be low?
Low levels can result from inherited genetic mutations, liver disease, pregnancy, or conditions that increase clotting activity (like severe infections or trauma). Your provider may investigate further based on your symptoms and medical history.
How often should I get this test?
Frequency depends on your health condition. If you have an inherited deficiency or a history of clotting disorders, your provider may recommend regular monitoring. Otherwise, this test is usually done as needed for specific situations (e.g., before surgery).
Can diet or supplements affect this test?
Dietary changes or supplements are unlikely to directly impact antithrombin III levels. However, if you’re on blood thinners (like warfarin), avoid supplements like ginkgo biloba or ginseng, as they may interact with medications.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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