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Serum or Plasma Antithrombin III Concentration (Mass 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 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
14470-9
Short code
C trach Ag Cvx Ql IA
Synonyms
C trach Ag Cvx 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
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 or conditions linked to abnormal clotting, such as deep vein thrombosis, pulmonary embolism, or unexplained bleeding. It may also be used to monitor treatment for inherited clotting disorders or to check for liver disease, which can affect protein production.

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 blood is drawn from a vein. If you’re taking blood from a fingerstick (e.g., for glucose monitoring), fasting isn’t required.

How the Test Is Performed

A healthcare professional will collect a blood sample from a vein in your arm using a needle. The sample is then sent to a lab for analysis.

What the Results Mean

Low levels of antithrombin III may indicate conditions like antithrombin III deficiency, liver disease, or certain medications that affect protein function. High levels could be due to pregnancy or certain medications. Your results will be compared to standard reference ranges provided by your lab.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III

Frequently asked questions

What causes antithrombin III levels to be low?
Low antithrombin III levels can result from inherited genetic disorders, liver disease (which affects protein synthesis), certain medications (like heparin or oral anticoagulants), or conditions like disseminated intravascular coagulation (DIC). Pregnancy may also temporarily increase its levels.
How often should I get this test?
The frequency depends on your medical condition. If you have a confirmed antithrombin III deficiency, your doctor may recommend testing every few months or annually. For monitoring treatment or monitoring symptoms, testing may be done less frequently, such as every 3–6 months.
Can I eat or drink before this test?
For blood drawn from a vein, fasting for 8–12 hours is typically recommended. If it’s a fingerstick (e.g., for glucose monitoring), no fasting is needed. Always follow your healthcare provider’s specific instructions.
  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