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Fluorescent Antibody Antibody Test for Antistreptolysin O (ASO) Antibodies (Serum)

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

This test measures antibodies in your blood that develop after a strep throat infection. It helps determine if you had recent strep bacteria exposure.

Quick summary

["ASO antibodies indicate past strep throat; not for diagnosing current infection."]

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

Key facts at a glance

LOINC
22096-2
Short code
FLUAV Ab Ser Ql
Synonyms
FLUAV 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 This Test Measures

ASO antibodies are produced by your immune system in response to *Streptococcus pyogenes* (group A strep) bacteria. These antibodies can stay in your blood for months after the infection clears, helping your body remember to fight future strep infections. This test detects their presence using a fluorescent antibody technique, which identifies specific immune proteins.

Why It’s Done

Doctors may order this test if you’ve had symptoms like sore throat, fever, or rash that suggest strep throat, especially if antibiotics weren’t effective. It’s also used in research or follow-up for people with recurrent strep infections or autoimmune conditions linked to strep exposure.

How It Works

A blood sample is drawn and tested for ASO antibodies using a fluorescent marker. If antibodies are present, they bind to the marker, creating a detectable signal that confirms their presence.

What to Expect

You’ll receive your results from your healthcare provider. A positive result suggests past strep exposure but doesn’t confirm an active infection. Follow-up testing may be needed for diagnosis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

ASO antibodies are important for diagnosing past strep infections and guiding treatment decisions. They’re also used in research to study autoimmune conditions like rheumatic fever or lupus, which may be linked to untreated strep. However, they’re not a direct measure of current infection status.

Short name

ASO Antibody Screening

Frequently asked questions

Can this test diagnose a current strep throat?
No. ASO antibodies indicate past exposure to strep bacteria, not an active infection. For diagnosing current strep throat, your doctor may use throat swab tests or other blood tests.
How long do ASO antibodies stay in my blood?
ASO antibodies can remain detectable for months to years after a strep infection. Their presence doesn’t necessarily mean you’re still contagious or at risk for complications like rheumatic fever.
What if my test is positive but I don’t have symptoms?
A positive ASO result means you likely had strep in the past. If you’re asymptomatic, it doesn’t mean you’re healthy, but it also doesn’t indicate an ongoing infection. Discuss with your doctor whether further testing or monitoring is needed.
  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