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Serum or Plasma Antithrombin III Concentration (Mass Concentration)

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

This test measures the amount of antithrombin III, a natural protein in your blood that helps prevent abnormal blood clotting.

Quick summary

["Antithrombin III helps regulate blood clotting and may be checked if you have a history of clotting disorders or bleeding problems."]

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

Key facts at a glance

LOINC
17587-7
Short code
ENA SS-B Ab Ser IF-aCnc
Synonyms
ENA SS-B Ab Ser IF-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
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 a history of blood clots, bleeding disorders, or if you’re taking medications that affect blood clotting. It can also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or hereditary antithrombin deficiency.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it’s drawn from serum, but plasma tests often don’t require fasting. Bring any medications or supplements you’re taking to your appointment.

How the Test Is Performed

A blood sample is drawn from a vein, usually in your arm, using a needle. The blood is then processed to separate serum or plasma for testing.

What the Results Mean

Results are compared to a reference range specific to your lab. Low levels may indicate an increased risk of clotting, while very low levels could signal a bleeding disorder or treatment side effect.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III Level

Frequently asked questions

What causes low or high antithrombin III levels?
Low levels may be due to hereditary deficiencies, liver disease, pregnancy, or certain medications. High levels are less common but can occur with liver disease or certain genetic conditions.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time.
Can I eat or drink before this test?
For serum tests, fasting for 8–12 hours is often recommended, but plasma tests may not require fasting. Always follow your healthcare provider’s 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