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Serum/plasma mass concentration of antithrombin III

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. It’s important for people with clotting disorders or those on blood thinners.

Quick summary

["Antithrombin III helps regulate blood clotting; low levels may increase clot risk."]

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

Key facts at a glance

LOINC
83112-3
Short code
PSA SerPl IA-mCnc
Synonyms
PSA SerPl IA-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0
Ref high
4
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
CPT
84153
SNOMED
39392002
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, are taking anticoagulant medications, or have conditions like liver disease that affect protein production. It can also be checked before surgeries or during pregnancy to monitor clotting risks.

What to Expect Before the Test

No special preparation is needed, but you may fast for 8–12 hours before the draw if instructed. Bring your medical records or medications to your appointment, as some drugs (like blood thinners) can affect results.

How the Test Works

A blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed to measure the protein concentration of antithrombin III using a specialized immunoassay method.

What the Results Mean

Results are compared to a reference range specific to your lab. Low levels may indicate liver disease, clotting disorders, or certain medications. High levels could suggest conditions like pregnancy or liver dysfunction. Always discuss results with your doctor.

Reference range

Normal: <4.0 ng/mLN/A

Specimen: serum

No special preparation required. For PSA, avoid sexual activity for 24-48 hours before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Antithrombin III Level

Frequently asked questions

What does a low antithrombin III level mean?
Low levels may raise your risk of blood clots, especially if you’re on blood thinners or have liver problems. Your doctor may adjust medications or monitor you more closely if results are below normal.
How do medications affect this test?
Certain anticoagulants (like warfarin) or drugs that affect liver function can change antithrombin III levels. Always tell your lab about all medications you’re taking to avoid misleading results.
When should I get this test retested?
If you recently had surgery, a blood clot diagnosis, or a change in medications, your doctor may recommend retesting. Follow-up is especially important if you’re pregnant or have a history of clotting issues.
  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