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Antibody Titration to Serologic Test for Antistreptolysin O (ASO)

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

This test measures the level of antibodies your body produces in response to a bacterial toxin called antistreptolysin O (ASO), often linked to Group A Streptococcus infections like strep throat or skin infections.

Quick summary

["Helps diagnose past or ongoing strep infections and guides treatment decisions."]

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

Key facts at a glance

LOINC
22568-0
Short code
ASO Ab Titr Ser
Synonyms
ASO Ab Titr Ser
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 Is ASO Testing Used For?

ASO testing is primarily used to identify whether you’ve had an infection caused by Group A Streptococcus (GAS), such as strep throat or impetigo. It can also help determine if symptoms persist despite antibiotics, suggesting a lingering infection or recurrence.

How Is the ASO Test Performed?

A blood sample is drawn from a vein in your arm. The serum (liquid part of blood) is then tested for ASO antibodies using an immunoassay method, which detects the presence and concentration of these antibodies.

What Does a Positive ASO Test Indicate?

A positive ASO test suggests recent or past exposure to Group A Streptococcus. High antibody levels may indicate an active infection, while lower levels could mean the body is clearing the infection or has already resolved it.

Interpreting Your Results

Results are typically reported as a titer value (e.g., 1:100, 1:200), indicating the highest dilution of serum where antibodies are detected. No specific reference ranges apply, but higher titers often correlate with more recent or severe infections.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

ASO Antibody Titer

Frequently asked questions

Why was I asked to take this test?
Your doctor may recommend this test if you have symptoms like sore throat, fever, rash, or swollen lymph nodes, or if you’ve been exposed to someone with a strep infection. It helps confirm or rule out strep and guides treatment, such as antibiotics.
What does a high ASO titer mean for my health?
A high ASO titer suggests you likely had a strep infection recently. While it doesn’t directly indicate complications like rheumatic fever (a rare but serious complication), it’s important for your doctor to monitor your symptoms and treatment response.
Can ASO test results change over time?
Yes, ASO antibody levels typically decline as the infection resolves. If your symptoms persist or return, retesting may be needed to check for recurrence or ongoing infection.
  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