Antibody to *Streptococcus* Group A (ASO) by Immunofluorescence
This test measures the presence of antibodies in your blood that your immune system produces in response to *Streptococcus* Group A bacteria, often linked to infections like strep throat or skin infections.
["Detects past or current strep infections that your body may have fought off."]
Key facts at a glance
- LOINC
- 29208-6
- Short code
- ASO Ab Fld-aCnc
- Synonyms
- ASO Ab Fld-aCnc
- Category
- coagulation
- 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
The ASO test identifies antibodies (specifically anti-streptolysin O) that your immune system creates after exposure to *Streptococcus* Group A bacteria. These antibodies can remain in your blood for months or even years after the infection has cleared, helping your body remember the threat for future protection.
Why It’s Ordered
Your healthcare provider may order this test if you have symptoms like sore throat, fever, rash, or joint pain that could suggest a strep infection. It’s also used to confirm a diagnosis when other tests (like rapid strep swabs) are inconclusive or if you’ve had recurrent infections.
What to Expect Before the Test
No special preparation is needed. You may have a simple blood draw from a vein in your arm, similar to other routine blood tests. If you’re concerned about needles, let your healthcare provider know so they can offer comfort measures.
What to Expect After the Test
After the blood is drawn, you may feel a slight pinch or bruising at the site, which usually fades within a day. There are no major side effects, but if you experience excessive bleeding or pain, contact your provider.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
A positive ASO test indicates your body has mounted an immune response to *Streptococcus* Group A, which can help diagnose past infections like scarlet fever, rheumatic fever, or post-streptococcal glomerulonephritis. However, it’s not always definitive for active infections, so your provider may combine results with other tests or symptoms to guide treatment.
Short name
ASO Antibody Test
Frequently asked questions
How long does it take to get results?
What does a high or low ASO level mean?
Can I take antibiotics before getting this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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