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Fluorescent Immunoassay for Antistreptolysin O Antibody (ASO) in Serum

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

This test measures antibodies your body produces in response to a bacterial infection caused by *Streptococcus* (group A strep). It helps diagnose recent strep throat or other strep-related infections.

Quick summary

["This test helps determine if you had a strep infection that your immune system is still reacting to."]

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

Key facts at a glance

LOINC
47458-5
Short code
FLUAV H9 Ab Titr Ser
Synonyms
FLUAV H9 Ab Titr Ser
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

Why This Test Is Done

Your doctor may order this test if you have symptoms like sore throat, fever, swollen lymph nodes, or rash, especially if strep throat is suspected. It can also be used to check for past infections in people with autoimmune conditions or recurrent infections.

How the Test Works

A small blood sample is taken from your arm. The serum (liquid part of blood) is then tested using a fluorescent immunoassay to detect specific antibodies (ASO) that your immune system creates in response to *Streptococcus* bacteria.

What to Expect Before the Test

No special preparation is needed, but let your doctor know if you’re on blood-thinning medications or have bleeding disorders, as this may affect blood collection.

What to Expect During the Test

You’ll lie down while a healthcare provider inserts a needle into your vein. The blood is drawn into a tube, and the serum is processed for testing. The process usually takes a few minutes.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

High ASO levels suggest recent strep infection, which can lead to complications like rheumatic fever if untreated. Low or absent levels indicate no recent infection or a resolved one. This test is particularly useful for confirming strep infections in children or adults with unclear symptoms.

Short name

ASO Antibody Test

Frequently asked questions

How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Your doctor will discuss the meaning of your results with you.
Can I drink or eat before this test?
You can eat and drink normally before this test unless instructed otherwise by your doctor. No fasting is required.
What if my ASO levels are elevated?
Elevated ASO levels often mean you had a strep infection recently. Your doctor may recommend antibiotics to treat the infection and monitor for complications like rheumatic fever. Follow-up tests may be needed if symptoms persist.
  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