What is this test?
Antistreptolysin O is an antibody that the body forms after contact with group A streptococci. The titer indicates an immune response, not the bacteria itself.
Why might it be ordered?
- When your clinician is assessing whether a previous streptococcal infection may be related to later joint, heart or kidney symptoms.
- To monitor the change in antibodies with a repeat sample if needed.
What sample is needed?
A healthcare professional collects a venous blood sample. Depending on the method, the laboratory uses serum or plasma.
How should you prepare?
Tell the laboratory about all medicines, hormone treatments, vitamins and supplements you take. Do not stop or change treatment unless your clinician tells you to. Follow any instructions about fasting and the time of collection.
How should you understand the result?
An elevated result supports recent or past contact but does not prove active infection. The change between two samples may be more informative than a single value. Your result is interpreted using the reference interval on the laboratory report and in the context of your symptoms, medical history and other test findings.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.
- Laboratory Tests — MedlinePlus, U.S. National Library of Medicine
- How to Prepare for a Lab Test — MedlinePlus, U.S. National Library of Medicine
- How to Understand Your Lab Results — MedlinePlus, U.S. National Library of Medicine
- Antibody Serology Tests — MedlinePlus, U.S. National Library of Medicine