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Antithrombin III Activity (Serum)

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

This test measures how well your blood naturally prevents clots from forming. Antithrombin III is a protein that helps regulate blood clotting.

Quick summary

["Helps assess your risk of abnormal blood clotting or bleeding disorders."]

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

Key facts at a glance

LOINC
46187-1
Short code
EHV2 Ab Titr Ser
Synonyms
EHV2 Ab Titr Ser
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 This Test Might Be Ordered

Your doctor may recommend this test if you have a history of blood clots, bleeding problems, or certain medical conditions like kidney disease or liver problems. It might also be checked before surgery or if you’re taking blood thinners.

What to Expect Before the Test

You’ll likely have a simple blood draw from a vein in your arm. No special preparation is needed, but tell your doctor about any medications or supplements you’re taking, as they could affect results.

How the Results Are Used

Low levels of antithrombin III can increase your risk of clots, while very low levels may suggest bleeding risks. Your doctor will interpret results in the context of your overall health and symptoms.

Common Conditions Monitored

This test helps diagnose or monitor conditions like disseminated intravascular coagulation (DIC), hereditary antithrombin deficiency, or conditions that may deplete antithrombin, such as severe infections or trauma.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

AT III Activity

Frequently asked questions

How long does it take to get results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing time. Follow-up with your doctor to review findings and next steps.
Can I eat or drink before this test?
No special diet or fasting is required for this blood test. However, inform your doctor about any recent medications or supplements you’ve taken, as they may affect results.
Is there any risk or discomfort with this test?
The blood draw may cause mild discomfort or bruising at the site, but complications are rare. Most people tolerate it well. If you have a hard-to-reach vein or are prone to bleeding, your doctor may use a different approach.
  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