Serum or Plasma Immunoassay for Anti-Streptolysin O Antibodies (ASO)

What Is the Purpose of This Test?

Doctors use the ASO test to confirm a strep throat diagnosis when symptoms like sore throat, fever, or swollen lymph nodes are present. It helps rule out other infections (like viral throat infections) and guides treatment decisions, such as prescribing antibiotics if needed.

How Is the Test Performed?

A blood sample is taken from a vein in your arm. The blood is then sent to a lab for testing using an immunoassay method, which detects the presence of ASO antibodies in your serum or plasma.

What Does a Positive Test Mean?

A positive ASO test suggests you likely had a recent strep throat infection. However, it may take a few weeks for antibodies to fully develop, so a negative result doesn’t always rule out strep. Follow-up testing or symptoms may be needed for confirmation.

What Are Common Results and Next Steps?

If your ASO test is positive, your doctor may recommend additional tests (like rapid strep swabs) or monitor symptoms closely. If negative, other causes of throat pain (like allergies or viral infections) may be considered. Antibiotics are not typically given based solely on ASO results unless strep is confirmed.