Skip to content

Fluorescent Immunoassay for Antistreptolysin O Antibodies (ASO) in Serum

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

This test measures the level of antibodies your body produces in response to certain bacterial infections, such as strep throat caused by Group A Streptococcus.

Quick summary

["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
74038-1
Short code
FLUAV H1 RNA Ct Spec Qn NAA+probe
Synonyms
FLUAV H1 RNA Ct Spec Qn NAA+probe
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
probe-amp-tar
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’ve had symptoms like sore throat, fever, or rash that could suggest a strep infection. It’s also used to check if you’ve recovered from strep or if you need further treatment.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from your arm. The blood is processed to separate serum, which is then tested for ASO antibodies using a fluorescent immunoassay method.

What the Results Mean

Higher levels of ASO antibodies indicate a recent strep infection. However, results alone don’t confirm the diagnosis—your doctor will consider symptoms, physical exam, and possibly other tests.

Common Causes of Positive Results

ASO antibodies appear after your body fights off a strep infection. They may stay elevated for weeks or months. Rarely, they can appear in other conditions like rheumatic fever or certain autoimmune diseases.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

ASO testing supports diagnosing strep infections, especially when throat cultures are unclear. Elevated levels may prompt additional treatment or monitoring for complications like rheumatic fever. It’s not a definitive test alone but helps guide care when combined with clinical judgment.

Short name

ASO Antibody Test

Frequently asked questions

What does a positive ASO test mean?
A positive ASO test suggests you likely had a strep infection recently, but it doesn’t confirm the diagnosis without other evidence. Your doctor will review your symptoms, exam, and possibly other tests to guide treatment.
Can ASO antibodies stay in my system long after the infection?
Yes, ASO antibodies can remain in your system for weeks or even months after the infection clears. They’re part of your immune response and don’t necessarily mean you’re still contagious or need ongoing treatment.
Is this test painful?
The blood draw for this test is mild discomfort for a few seconds, similar to other routine blood tests. Most people tolerate it well, and any soreness fades quickly.
  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