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Serum Anti-Streptolysin O (ASO) Antibody, Quantitative

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

This test measures the level of antibodies your body produces in response to a bacterial infection caused by Group A Streptococcus (strep throat or scarlet fever). It helps diagnose past infections and assesses immune response.

Quick summary

["Helps identify strep infections and immune reaction over time."]

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

Key facts at a glance

LOINC
5184-7
Short code
HAV Ab Ser RIA-aCnc
Synonyms
HAV Ab Ser RIA-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
ria
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

What Is This Test Measuring?

The ASO test detects antibodies called anti-streptolysin O (ASO) in your blood. These antibodies develop after your immune system fights off Group A Streptococcus bacteria, which can cause infections like strep throat or skin infections. The test helps determine if you’ve had a recent or past infection.

Why Might You Need This Test?

Your healthcare provider may order this test if you have symptoms of a strep infection (e.g., sore throat, fever, swollen lymph nodes) or if you’ve been exposed to Group A Streptococcus. It can also help confirm a diagnosis when other tests are inconclusive or monitor treatment effectiveness.

How Is the Test Performed?

A blood sample is taken from a vein in your arm. The sample is sent to a lab for analysis using an immunoassay method to measure the ASO antibody concentration.

What Are the Results Typically Used For?

High ASO levels suggest a recent Group A Streptococcus infection. Rising or falling levels over time can indicate the body’s immune response to treatment or healing. Results are used alongside clinical symptoms to guide diagnosis and management.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance:

Short name

ASO Antibody Test

Frequently asked questions

How long does it take for ASO levels to rise after a strep infection?
ASO levels typically begin to rise about 7–10 days after infection and may remain elevated for weeks or months, depending on the severity and immune response. They usually peak around 2–3 weeks post-infection and gradually decline as the body clears the bacteria.
Can ASO levels be affected by other conditions or medications?
ASO levels are specific to Group A Streptococcus infections. While other infections or conditions (like rheumatic fever) may be associated with similar symptoms, ASO testing is not affected by unrelated illnesses or medications unless they suppress the immune system.
What should I do if my ASO test result is elevated?
If your ASO test result is elevated, your healthcare provider may recommend further testing (e.g., rapid strep test) or additional follow-up to confirm the diagnosis. Treatment with antibiotics (like penicillin) is often prescribed to clear the infection and prevent complications like rheumatic fever.
  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