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Serum Antithrombin III Activity (Qualitative or Quantitative)

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

This test measures the level of antithrombin III, a natural protein in your blood that helps prevent abnormal blood clots from forming.

Quick summary

["Antithrombin III plays a key role in blood clotting regulation; low levels may increase clot risk or affect treatment effectiveness."]

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

Key facts at a glance

LOINC
110754-9
Short code
ENA SS-A IgG Msmt Ser
Synonyms
ENA SS-A IgG Msmt Ser
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 are taking medications that affect clotting. It may also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or hereditary thrombophilia.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications or supplements that could affect results. Fasted or non-fasted blood draws are often acceptable, depending on the lab’s protocol.

How the Test Works

Blood is drawn from a vein, typically in your arm. The sample is sent to a lab where it is tested for antithrombin III activity using an immunoassay or similar method to measure its function.

What the Results Mean

Results are often reported as a percentage or ratio relative to a standard. Low levels may indicate a deficiency that increases clot risk, while normal levels suggest adequate protection against abnormal clotting.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Antithrombin III (ATIII) Test

Frequently asked questions

What Are Common Causes of Low or High Results?
Low antithrombin III levels can be caused by genetic disorders, liver disease, pregnancy, or certain medications. High levels may rarely occur due to conditions like acute phase reactions (e.g., infection) or overproduction in some liver disorders.
How Might My Results Affect My Treatment?
If your results show a deficiency, you may need lifelong treatment with antithrombin concentrates or other interventions to manage clot risk. Follow-up tests may be scheduled to monitor your levels over time.
Will I Need to Avoid Certain Foods or Activities Before the Test?
No specific dietary restrictions apply, but avoid excessive alcohol or medications that alter clotting (e.g., NSAIDs) unless directed by your provider. Rest assured that the test is generally safe and does not require special precautions.
  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