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Immunoassay for IgG Antibody to Group A Streptococcus (Anti-Streptolysin O, ASO)

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

This blood test measures antibodies produced in response to Group A Streptococcus bacteria, often linked to strep throat or other infections.

Quick summary

["Helps diagnose past strep infections and guides treatment decisions."]

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

Key facts at a glance

LOINC
107730-4
Short code
Goat Milk IgG Qn IA
Synonyms
Goat Milk IgG Qn 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
CPT
82784
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 Is Done

Your doctor may order this test if you have symptoms like sore throat, fever, or rash that could suggest Group A Streptococcus infection (e.g., strep throat, scarlet fever). It can also be used to check for past infections in people with rheumatic fever or other autoimmune conditions linked to strep exposure.

How the Test Works

A small blood sample is taken from your arm. The lab uses an immunoassay to detect specific antibodies (ASO) your immune system produces after exposure to Group A Streptococcus bacteria. These antibodies are a marker of past infection.

What to Expect Before the Test

No special preparation is needed. You may eat and drink as usual, but inform your doctor if you’re on blood-thinning medications or have bleeding disorders.

What the Results Mean

High levels of ASO antibodies suggest a past Group A Streptococcus infection. However, results alone don’t confirm the current infection—your doctor will consider symptoms, culture results, and other factors.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

ASO Antibody Test

Frequently asked questions

What does a positive result mean?
A positive ASO test indicates your body has likely been exposed to Group A Streptococcus bacteria in the past. This can help diagnose conditions like rheumatic fever or guide treatment for recurrent strep throat. However, it’s not definitive for active infection without clinical correlation.
Can this test detect active strep throat?
No, this test measures antibodies from past infections, not active bacteria. For diagnosing active strep throat, your doctor may use throat cultures or rapid antigen tests instead.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on lab processing times. Follow up with your doctor to discuss findings and next steps.
  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