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Total Antithrombin III Activity (Serum)

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

This test measures the level of antithrombin III, a naturally occurring 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 problems."]

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

Key facts at a glance

LOINC
32998-7
Short code
tTG IgG Ser-aCnc
Synonyms
tTG IgG Ser-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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 recommend this test if you have symptoms like easy bruising, excessive bleeding, or a history of blood clots. It could also be part of a screening or monitoring plan for conditions like disseminated intravascular coagulation (DIC) or inherited clotting disorders.

What to Expect Before the Test

No special preparation is needed for this test. You may have a small needle inserted into your arm to draw blood. If you’re on blood thinners, let your provider know before the test.

What the Results Mean

Low levels of antithrombin III may indicate an increased risk of blood clots, while very low levels could suggest a genetic disorder or other underlying health issue. Results are compared to a standard range for your age and sex.

Common Conditions Monitored

This test is often used to diagnose or monitor conditions like antithrombin deficiency, liver disease, or after treatments that may affect blood clotting, such as chemotherapy.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III

Frequently asked questions

What are the normal reference ranges for this test?
Reference ranges can vary by lab and may depend on factors like age, sex, and health status. Your provider will discuss your specific results with you.
How often should I get this test?
Your provider will determine how often you need this test based on your medical history, symptoms, and treatment plan. Follow their guidance closely.
Can I eat or drink before this test?
You can eat and drink normally before this test unless your provider gives specific instructions. Blood tests are typically done on an empty stomach for some tests, but this one does not require fasting.
  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