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Fluorescent Immunoassay for Antistreptolysin O Antibody (ASO)

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

This test measures the presence of antibodies your body produces in response to certain bacterial infections, specifically Group A Streptococcus (strep throat or scarlet fever).

Quick summary

["ASO helps diagnose past or recent strep infections and guides treatment decisions."]

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

Key facts at a glance

LOINC
41138-9
Short code
FLUAV N5 Ab Ser Ql
Synonyms
FLUAV N5 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 ASO Test Used For?

Doctors may use the ASO test to confirm a strep infection if symptoms like sore throat, fever, or rash are present. It can also help determine if you had strep in the past, even if you don’t remember symptoms.

How Is the ASO Test Performed?

A blood sample is taken from a vein in your arm. The blood is then tested using a fluorescent immunoassay method to detect ASO antibodies.

What Does a Positive ASO Test Mean?

A positive result suggests you’ve had a recent or past Group A strep infection. It doesn’t always indicate active infection now, but it can help guide treatment if needed.

What Does a Negative ASO Test Mean?

A negative result means you likely haven’t had a recent strep infection or your body hasn’t produced enough ASO antibodies yet.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

ASO Antibody Test

Frequently asked questions

Why might my doctor order an ASO test?
Your doctor may order this test if you have symptoms like sore throat, fever, or rash that suggest strep infection, or if you’ve had strep in the past and need confirmation.
What are the possible side effects of the blood draw?
You may feel slight discomfort or bruising at the injection site, but most people experience only minor pain or swelling. Rarely, there could be a small risk of infection or excessive bleeding.
How soon will I get my results?
Results are typically available within 24 to 48 hours, depending on lab processing times. Your doctor will discuss them with you during your follow-up visit.
  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