Skip to content

Serum or plasma concentration of antithrombin III

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

This test measures the amount 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 a history of clotting disorders or bleeding issues."]

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

Key facts at a glance

LOINC
17585-1
Short code
ENA SS-A IgG Ser Ql IA
Synonyms
ENA SS-A IgG Ser Ql IA
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
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 Is This Test Done?

Your healthcare provider may order this test if you have symptoms like easy bruising, excessive bleeding, or a history of blood clots. It may also be checked before certain surgeries or treatments that affect blood clotting.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood from a vein.

What Happens During the Test?

A healthcare professional will insert a small needle into a vein in your arm to draw blood. You may feel a brief pinch, but it usually doesn’t cause discomfort. The blood sample is then sent to a lab for testing.

What Are Possible Results?

Results are reported as a concentration level of antithrombin III in the blood. Lower than normal levels may indicate an increased risk of clotting, while higher levels may suggest bleeding tendencies or certain medical conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Antithrombin III plays a critical role in blood coagulation. Low levels can be linked to inherited or acquired clotting disorders, while elevated levels may be associated with bleeding disorders or conditions like liver disease. Regular monitoring may be needed if you’re on anticoagulant medications.

Short name

Antithrombin III Level

Frequently asked questions

What does a low antithrombin III level mean?
A low level may increase your risk of blood clots and could require medical evaluation to determine if you need treatment or monitoring.
How is antithrombin III tested?
The test involves drawing blood from a vein and measuring the protein’s concentration using an immunoassay or similar method.
Can I eat or drink before this test?
Check with your provider about fasting requirements, but generally, you can eat a light meal unless instructed otherwise.
  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