Antistreptolysin O titre (ASO)

What it measures

Measures antibody against streptolysin O, a toxin of group A streptococci. It supports diagnosis of recent streptococcal infection and its complications.

Specimen and preparation

• Specimen: Serum
• Tube: Red top

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Recent group A streptococcal pharyngitis
• Acute rheumatic fever
• Post-streptococcal glomerulonephritis
• Scarlet fever

Method

Latex agglutination (semi-quantitative) or immunoturbidimetry

Good to know

Titres peak 3–5 weeks after infection; skin infections raise anti-DNase B more than ASO.

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