What does the Anti-Streptolysin O Antibody test measure?

Why is Anti-Streptolysin O Antibody measured?

ASO is not used to diagnose acute streptococcal pharyngitis — throat culture or rapid antigen detection serve that purpose — but rather to document recent group A streptococcal infection when a clinician suspects a post-infectious sequela such as acute rheumatic fever or post-streptococcal glomerulonephritis. A rising titre between acute and convalescent samples provides stronger evidence than a single elevated value, because background seroprevalence in the general population means that many healthy individuals carry detectable titres from past exposures.

Reference ranges

Standard reference

≤200 IU/mL in adults and school-age children; varies by age and season.

Functional medicine optimal

No 'optimal' range applies; the clinical question is whether a titre is elevated relative to age-specific norms and whether it rises or falls between serial samples.

Units

IU/mL, Todd units

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.