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Serum Antithrombin III Concentration (Mass)

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

This test measures the amount of antithrombin III, a natural protein in your blood that helps prevent abnormal blood clotting.

Quick summary

["Antithrombin III helps maintain healthy blood flow by regulating clotting processes."]

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

Key facts at a glance

LOINC
17584-4
Short code
ENA SS-A Ab Ser IF-aCnc
Synonyms
ENA SS-A Ab Ser IF-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
if
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

What Is Antithrombin III?

Antithrombin III is a protein produced by your liver that acts as an inhibitor of clotting factors. It helps prevent blood from clotting too quickly or forming dangerous clots in places like arteries or veins. Low levels can increase your risk of clotting disorders.

Why Might You Need This Test?

Your doctor may order this test if you have a history of blood clots, certain medical conditions (like liver disease), or if you’re taking medications that affect clotting. It can also help monitor treatment for conditions like disseminated intravascular coagulation (DIC).

How Is the Test Performed?

A blood sample is drawn from a vein, usually in your arm. The blood is then processed to separate serum (the liquid part after clotting) for testing. The test measures the protein’s concentration using a specialized laboratory method.

What Do Results Mean?

Results are compared to a standard range for healthy adults. Very low levels may indicate conditions like liver disease, clotting disorders, or certain medications affecting protein production. Very high levels may rarely suggest conditions like multiple myeloma or pregnancy.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Why It Matters

Short name

Antithrombin III

Frequently asked questions

How often will I need this test?
This test is typically ordered as needed, depending on your medical condition or treatment plan. Your doctor will determine how often you need retests, if at all. Follow-up may be scheduled if you’re on medications that affect clotting or if you have ongoing symptoms.
What are the normal reference ranges?
Reference ranges can vary by lab and may not be widely publicized. Your results will be interpreted by your healthcare provider based on your specific situation.
Can I eat or drink before this test?
You may eat and drink normally before the test unless instructed otherwise by your doctor. Avoid alcohol for 24 hours before the test, as it may affect blood clotting.
  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