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Total Antithrombin III Concentration (Serum or Plasma)

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. Low levels may indicate a higher risk of clotting disorders.

Quick summary

["Antithrombin III helps regulate blood clotting; low levels may signal clotting risks or liver issues."]

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

Key facts at a glance

LOINC
22187-9
Short code
C trach Ab Titr Ser
Synonyms
C trach 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 Matters

Antithrombin III is a crucial protein that inhibits clotting factors to maintain healthy blood flow. When levels are too low, you may be at increased risk of blood clots, especially in conditions like deep vein thrombosis (DVT) or pulmonary embolism. It’s also important if you’ve had a history of clotting problems or liver disease, as both can affect its production.

What to Expect Before the Test

No special preparation is needed unless instructed by your healthcare provider. You may have a small needle inserted into a vein in your arm to draw blood. If you’re taking blood thinners, let your provider know before testing.

What the Results Mean

Results are compared to a standard range for healthy individuals. Very low levels may indicate conditions like antithrombin deficiency, liver disease, or certain infections. Very high levels are less common but could suggest rare genetic disorders.

Common Conditions Monitored

Doctors may order this test if you have a history of blood clots, unexplained bleeding, liver problems, or if you’re taking anticoagulant medications. It’s also used to monitor treatment for inherited clotting disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III Level

Frequently asked questions

How often do I need this test?
Your doctor will determine how often you need this test based on your medical history, symptoms, and treatment plan. For example, if you have a known clotting disorder, you may need regular monitoring. If you’re healthy, it’s usually only ordered if symptoms or risk factors arise.
What are the typical reference ranges?
Reference ranges can vary by lab, but healthy levels are generally between 70% and 150% of a standard reference value. Your specific range will be provided with your results.
Can I eat or drink before this test?
You can eat and drink normally before the test unless your provider advises otherwise. Avoid alcohol for at least 24 hours before testing, as it may affect blood clotting proteins.
  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