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

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

This test measures the level of antibodies your body produces in response to Group A Streptococcus bacteria, often linked to strep throat or other infections.

Quick summary

["Helps diagnose or monitor strep infections and rheumatic fever risk."]

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

Key facts at a glance

LOINC
6555-7
Short code
S pneum Ag Spec Ql IF
Synonyms
S pneum Ag Spec Ql IF
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
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 the ASO Test Used For?

Doctors may order this test to confirm a Group A Streptococcus infection (like strep throat) when symptoms like sore throat, fever, or swollen lymph nodes are present. It can also help assess whether you’ve had a recent strep infection and whether you’re at risk for complications like rheumatic fever, a rare but serious condition that can affect the heart and joints.

How Is the ASO Test Performed?

A blood sample is taken from a vein in your arm. The blood is then sent to a lab where it’s tested for ASO antibodies using an immunoassay method. Results are typically available within 24–48 hours.

What Does a Positive ASO Test Mean?

A positive ASO test indicates your immune system has produced antibodies against Group A Streptococcus, suggesting you’ve likely had a recent strep infection. However, it doesn’t always mean you’re currently infected—antibodies can remain in your system for weeks or months after the infection clears.

When Might You Need Follow-Up Testing?

If your ASO test is positive and you have symptoms like joint pain, heart palpitations, or a rash, your doctor may recommend further evaluation to rule out rheumatic fever or other complications. Follow-up tests or monitoring may also be needed if you’ve had repeated strep infections.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: ASO Antibodies and Health Risks

Short name

ASO Antibody Test

Frequently asked questions

Why was my ASO test ordered?
Your doctor may have ordered this test to diagnose a strep infection, check for recent exposure to Group A Streptococcus, or assess your risk of developing rheumatic fever—especially if you’ve had repeated strep throat episodes or symptoms like joint pain or fatigue.
What do my ASO test results mean for my health?
A positive ASO test confirms past or recent strep infection but doesn’t always indicate an active infection. If you’re concerned about complications like rheumatic fever, discuss your results with your doctor. They may recommend additional tests or treatments based on your symptoms and medical history.
Can ASO test results change over time?
Yes, ASO antibody levels can decline over weeks or months after a strep infection. If your test is positive but symptoms persist, your doctor may retest or investigate other causes of your condition.
  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