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Serum or Plasma Anti-Streptolysin O (ASO) Antibody, Quantitative

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

This test measures the amount of antibodies your body produces in response to a bacterial infection caused by Group A Streptococcus (strep throat or scarlet fever). It helps diagnose past infections or assess ongoing immune response.

Quick summary

["The ASO test helps identify strep infections and guide treatment decisions."]

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

Key facts at a glance

LOINC
11269-8
Short code
S pyo Ag Ser Ql Aggl
Synonyms
S pyo Ag Ser Ql Aggl
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
aggl
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 recently had symptoms like sore throat, fever, rash, or swollen lymph nodes—common signs of strep throat or scarlet fever. It’s also used to check if you’ve recovered from a strep infection or if your immune system is still responding to it.

How the Test Works

Blood is drawn, and the lab tests it for ASO antibodies using an immunoassay method. These antibodies appear in your blood after your immune system fights off Group A Streptococcus bacteria.

What to Expect Before the Test

No special preparation is needed. You may have a slight bruise or soreness at the injection site, but this usually fades quickly. If you’re on blood-thinning medication, let your doctor know before the test.

What the Results Mean

Higher levels of ASO antibodies suggest a recent strep infection. Very high levels may indicate an ongoing immune response, while lower levels could mean the infection has cleared or you’re not infected now.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

ASO Antibody Test

Frequently asked questions

How long does it take to get results?
Results are typically available within 24 to 48 hours, depending on your lab’s processing time. Your doctor will discuss them with you during your follow-up visit.
Can I take antibiotics before the test?
Yes, but inform your doctor beforehand. Antibiotics can lower ASO levels, so timing may affect the test’s accuracy. Your doctor will help decide the best time to retest if needed.
Is this test painful?
No, the blood draw is quick and mild discomfort is common. Most people feel little to no pain afterward. If you’re anxious, ask about numbing cream or other comfort measures.
  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