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Serum Antithrombin III (ATIII) Concentration

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

This test measures the level 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 or are at risk for clotting disorders."]

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

Key facts at a glance

LOINC
5226-6
Short code
HTLV I+II Ab Ser IA-aCnc
Synonyms
HTLV I+II 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 Might Be Ordered

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 your liver. It could also be done before surgeries or treatments that increase your risk of clotting, or if you’re being evaluated for conditions like disseminated intravascular coagulation (DIC).

What to Expect Before the Test

No special preparation is usually needed. You may have a small needle inserted into your arm to draw a blood sample. If you’re on blood thinners or have a history of bleeding issues, let your provider know before the test.

What the Results Mean

Low levels of antithrombin III can indicate an increased risk of blood clots, while very low levels may suggest liver disease or other conditions affecting protein synthesis. Results are compared to a general reference range for healthy adults.

Common Conditions Affecting Results

Conditions like liver disease, kidney problems, or certain medications (such as oral contraceptives or hormone therapy) can lower antithrombin III levels. Repeating the test after treatment or changes in health may be recommended.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III

Frequently asked questions

How often should I get this test?
The frequency depends on your health status. If you have a known clotting disorder or are under treatment, your provider may recommend regular monitoring. Otherwise, this test is often done as needed for specific situations, such as pre-surgery or during active treatment for clotting risks.
What does a low result mean for my treatment?
A low result may prompt your provider to adjust your treatment plan, such as changing medications, increasing anticoagulant therapy, or investigating underlying causes like liver disease. Follow-up tests or additional evaluations may be needed.
Can I eat or drink before this test?
You can eat and drink normally before this test unless your provider instructs otherwise. Blood tests like this are typically done on an empty stomach only if the test requires fasting for other reasons, which is not the case here.
  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