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Fluorescent Antibody Assay for Antistreptolysin O Antibodies (ASO)

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

This test measures antibodies your immune system produces in response to certain bacterial infections, specifically *Streptococcus* (group A). It helps assess past or recent strep throat or other streptococcal infections.

Quick summary

["This test helps diagnose or monitor strep-related conditions by detecting immune system responses to bacterial toxins."]

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

Key facts at a glance

LOINC
41134-8
Short code
FLUAV N9 Ab Ser Ql
Synonyms
FLUAV N9 Ab Ser Ql
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 the Purpose of This Test?

Your healthcare provider may order this test if you’ve had symptoms like sore throat, fever, or rash that could suggest strep infection. It’s also used to check for past infections or guide treatment decisions in certain cases.

How Is the Sample Collected?

A blood sample is drawn from a vein in your arm. The blood is processed to separate serum (liquid part of blood) for testing.

What Does a Positive Result Mean?

A positive result indicates your body has produced ASO antibodies, suggesting you’ve been exposed to *Streptococcus* bacteria. This can confirm a past strep infection or help track immune response over time.

What Are Common Causes of Abnormal Results?

High levels may appear after strep throat, scarlet fever, or other streptococcal infections. Rarely, they can be elevated in other inflammatory conditions or with certain autoimmune diseases.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: This test supports diagnosis of streptococcal infections by identifying immune markers. It’s particularly useful when cultures or rapid tests are unavailable or inconclusive. Results may guide antibiotic selection or monitor treatment response.

Short name

ASO Antibody Test

Frequently asked questions

Why might my doctor want to check ASO levels repeatedly?
If you’ve had recurrent strep infections or certain autoimmune conditions, your doctor may monitor ASO levels to track immune activity or assess long-term effects of past infections.
Can ASO levels be affected by other medications?
Some antibiotics (like penicillin) or immune-modulating drugs may influence antibody production, but ASO testing itself isn’t directly affected by medications.
How soon after infection might I see results?
Results typically appear 1–2 weeks after infection, as your immune system takes time to produce detectable antibodies. Results may take longer to normalize after treatment.
  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