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Serum or Plasma Antithrombin III 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 abnormal 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
31772-7
Short code
C trach Ag Vag Ql
Synonyms
C trach Ag Vag Ql
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 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 done before certain surgeries or treatments that affect blood clotting.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if your lab requires it. Avoid aspirin or blood thinners for 48 hours unless directed otherwise.

How the Test Is Performed

A healthcare professional will draw blood from a vein in your arm. The blood sample is sent to a lab for analysis using an immunoassay method to measure antithrombin III levels.

What the Results Mean

Results are reported as a percentage or mass concentration relative to a standard. Low levels may indicate a higher risk of clotting, while very low levels could suggest bleeding disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III

Frequently asked questions

What causes abnormal antithrombin III levels?
Abnormal levels can result from genetic mutations, liver disease, kidney problems, or certain medications (like heparin or anticoagulants). Infections, pregnancy, or trauma may also temporarily affect levels.
What treatments or lifestyle changes might help?
If levels are low, your doctor may recommend blood thinners, dietary adjustments (like increasing vitamin K), or monitoring. Lifestyle changes such as avoiding smoking and managing weight may also support healthy clotting.
Can antithrombin III levels change with diet?
Yes, certain foods or supplements (like vitamin K) can influence clotting proteins, but antithrombin III itself is not directly affected by diet. Follow your doctor’s advice on dietary restrictions if needed.
  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