What does the Anti-streptolysin O Antibody test measure?

Why is Anti-streptolysin O Antibody measured?

ASO is a marker of recent or ongoing group A streptococcal infection and the principal serological test for confirming post-streptococcal sequelae. It is central to the diagnosis of acute rheumatic fever (where an elevated or rising titre supports one of the Jones major criteria) and post-streptococcal glomerulonephritis. Because ASO may remain normal after skin infections (impetigo, cellulitis), anti-DNase B is the preferred marker in that setting. Isolated elevated titres are common and do not diagnose rheumatic fever or glomerulonephritis without the corresponding clinical syndrome.

Reference ranges

Standard reference

Typically <200 IU/mL in adults, <100 IU/mL in children under five; assay- and age-specific.

Functional medicine optimal

There is no therapeutic 'optimal' ASO titre; the value is interpreted in the context of suspected post-streptococcal disease, and a rising titre (fourfold change between acute and convalescent specimens) is more informative than a single elevated result.

Units

IU/mL, Todd units, Todd units/mL

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