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Antithrombin III Activity (Serum)

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

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

Quick summary

["Antithrombin III supports blood flow and reduces clot risk by inhibiting clotting factors."]

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

Key facts at a glance

LOINC
32716-3
Short code
ENA SS-A Ab Titr Ser
Synonyms
ENA SS-A 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 Is Done

Your doctor may order this test if you have a history of blood clots, certain blood disorders, or conditions that affect protein production in the liver. It can also be part of routine monitoring for people on anticoagulant therapy or those with inherited clotting disorders.

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 your arm.

How the Test Works

A small needle is inserted into a vein in your arm to draw blood. The sample is then tested to measure how well antithrombin III can stop clotting in the lab.

Possible Results and Their Meaning

Results are expressed as a percentage or ratio compared to a standard. Low levels may indicate a higher risk of clotting, while normal levels suggest healthy blood flow regulation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Antithrombin III Activity

Frequently asked questions

What Does a Low Level Mean?
Low antithrombin III activity can increase your risk of blood clots, especially if you have conditions like liver disease, kidney disease, or certain medications that deplete this protein.
What Does a High Level Mean?
High levels are less common but may occur in rare genetic disorders or during pregnancy. Your doctor will discuss findings in the context of your overall health.
How Often Should I Get This Test?
Your doctor will determine how often you need this test based on your medical history, treatment plan, or symptoms. Follow-up may be scheduled if you’re on anticoagulants or have a clotting disorder.
  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