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Serum or Plasma Substance Concentration (Electrochemiluminescence Immunoassay) for Antithrombin III

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.

Quick summary

["Antithrombin III helps regulate blood clotting and may be checked if you have a history of clotting disorders or bleeding issues."]

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

Key facts at a glance

LOINC
3239-1
Short code
Fact XIII Ag Act/Nor PPP IA
Synonyms
Fact XIII Ag Act/Nor PPP IA
Category
chemistry
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
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 Might Be Ordered

Your healthcare provider may order this test if you have symptoms like easy bruising, excessive bleeding, or a history of blood clots. It may also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or hereditary antithrombin deficiency.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood from a vein. Avoid smoking or consuming alcohol for at least 1 hour before the procedure.

What Happens During the Test

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure usually takes only a few minutes. The blood sample is then sent to a lab for analysis using an immunoassay method.

What the Results Mean

Results are compared to a reference range, which can vary by lab. Low levels of antithrombin III may indicate an increased risk of blood clots, while very low levels could suggest a bleeding disorder. Your provider will discuss results in the context of your medical history and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Antithrombin III (ATIII) Level

Frequently asked questions

What Does This Test Measure?
This test measures the concentration of antithrombin III, a protein that inhibits blood clotting. It helps identify whether your blood has normal or altered clotting function, which can inform treatment decisions for conditions like clotting disorders or bleeding risks.
When Might My Results Be Abnormal?
Results may be abnormal if your levels are significantly lower than expected, which could be due to genetic factors, liver disease, pregnancy, or certain medications. Abnormal results may prompt further testing or adjustments to your treatment plan.
How Often Should I Get This Test?
Your provider will determine how often you need this test based on your medical needs, such as monitoring treatment for a clotting disorder or assessing risk factors like pregnancy or surgery. Follow their guidance for follow-up testing.
  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