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Antithrombin III Activity (Serum/Plasma)

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

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

Quick summary

["Antithrombin III helps maintain healthy blood flow by inhibiting clotting factors."]

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

Key facts at a glance

LOINC
53016-2
Short code
ENA SS-A 52kD Ab Ser Ql
Synonyms
ENA SS-A 52kD Ab Ser Ql
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 Is This Test Done?

Your doctor may order this test if you have a history of blood clots, bleeding problems, or certain medical conditions like liver disease or kidney problems. It can also be checked before surgeries or treatments that increase the risk of clotting.

What Does a Result Mean?

Results are typically reported as a percentage or ratio relative to a standard. Low levels may indicate an increased risk of clotting, while very low levels can lead to bleeding issues. Your doctor will interpret the result in the context of your overall health.

Common Conditions Monitored

This test is often used to monitor conditions like disseminated intravascular coagulation (DIC), hereditary antithrombin deficiency, or after treatments that affect blood clotting, such as heparin therapy.

Sample Collection and Preparation

A blood sample is drawn from a vein, usually in your arm. The blood is collected in a tube that prevents clotting and then sent to a lab for testing. Plasma or serum is used, depending on the method used for analysis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Antithrombin III plays a critical role in regulating blood clotting. Low levels can increase the risk of clotting events, such as deep vein thrombosis or pulmonary embolism, while high levels may not be clinically significant unless part of a broader evaluation for bleeding disorders.

Short name

Antithrombin III

Frequently asked questions

What causes low antithrombin III levels?
Low antithrombin III levels can be caused by genetic disorders, liver disease, kidney disease, certain medications (like heparin), or conditions that increase blood clotting, such as pregnancy or severe infections.
How is antithrombin III treated if it’s low?
If levels are low, treatment may include medications to prevent clots, such as anticoagulants, or replacement therapy with antithrombin III concentrates in severe cases. Your doctor will determine the best approach based on your specific situation.
Can antithrombin III levels change over time?
Yes, antithrombin III levels can fluctuate due to medical conditions, treatments, or lifestyle factors. Regular monitoring is important if you have a history of clotting disorders or are undergoing treatments that 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