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Serum or Plasma Substance Concentration (Electrochemiluminescence Immunoassay) for Antithrombin III Activity

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

This test measures the level of antithrombin III (ATIII), a natural protein in your blood that helps prevent blood clots from forming. Low levels may increase your risk of clotting.

Quick summary

["Antithrombin III helps regulate blood clotting; low levels may raise clot risk and require monitoring or treatment."]

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

Key facts at a glance

LOINC
63352-9
Short code
ENA SM Ab Fld Ql ID
Synonyms
ENA SM Ab Fld Ql ID
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
immune-diffusion
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 doctor may recommend this test if you have a history of blood clots, certain blood disorders, or are taking medications that affect clotting. It may also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or after surgery.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for a few hours before the blood draw. Wear a loose shirt for easy access to your arm.

What Happens During the Test

A healthcare professional will insert a small needle into a vein in your arm to draw a blood sample. You may feel a brief pinch, but the procedure is quick and typically painless.

What the Results Mean

Results are compared to a standard range to determine if your ATIII levels are within normal limits. Very low levels may indicate conditions like liver disease or inherited clotting disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III Activity

Frequently asked questions

What does a low result indicate?
A low antithrombin III level may suggest an inherited or acquired condition that increases your risk of blood clots. This could be due to liver disease, kidney problems, or certain medications.
What does a high result indicate?
High levels of antithrombin III are generally not clinically significant unless associated with other conditions or symptoms. Very high levels are rare but may occur in some genetic disorders.
How often will I need this test?
Your doctor will determine how often you need this test based on your medical history, treatment plan, and symptoms. Regular monitoring may be required if you have a history of clotting issues or are taking anticoagulant medications.
  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