Lab marker · Low

Low Anti-streptolysin O (ASO): what it means

A Anti-streptolysin O (ASO) result below the normal range is considered low. Here is what a reduced Anti-streptolysin O (ASO) can point to, and when it is worth discussing with a doctor.

Reference range: typically <200 IU/mL in adults; a raised or rising level is evidence of a recent group A streptococcal infection — used mainly to support a diagnosis of rheumatic fever or post-strep kidney inflammation, not to diagnose an active sore throat

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What a low Anti-streptolysin O (ASO) can mean

  • Normal or low — no evidence of recent strep infection.
  • A skin (rather than throat) strep infection — ASO can be less reliably raised, so anti-DNase B may be more useful.
  • Very early in an illness — the antibody may not have risen yet; a repeat sample can help.

When to discuss with a doctor

ASO is not a test for a current sore throat — a throat swab or rapid strep test is used for that. Instead it is requested when a doctor is investigating a possible complication of a recent strep infection, such as new joint pains, a heart murmur or signs of rheumatic fever, or blood and protein in the urine suggesting post-streptococcal kidney inflammation. A raised or, better, a rising ASO supports that a strep infection was the trigger, and is interpreted with the clinical picture and often a second antibody test. A high ASO on its own, without symptoms, usually just reflects a past infection and needs no action. Mediora.AI shows ASO alongside inflammatory markers so the post-strep pattern is visible; the interpretation and any diagnosis belong with your doctor.

Conditions this can relate to

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Mediora.AI is informational - interpretation, not a diagnosis. A single out-of-range value is common and often benign; always discuss decisions with your doctor.