What is the treatment for a high Antistreptolysin O (ASO) titre?

Treatment of Elevated ASO Titre

An elevated ASO titre itself does not require treatment—the focus must be on identifying and treating the underlying post-streptococcal complication (acute rheumatic fever or post-streptococcal glomerulonephritis) if present, with antibiotic therapy aimed at eradicating residual Group A Streptococcal infection to prevent permanent cardiac damage. 1

Understanding What ASO Titre Represents

• ASO titre is a marker of past streptococcal infection, not active disease requiring direct treatment. 1, 2
• The test reflects an immunologic response that begins rising approximately 1 week after infection and peaks at 3-6 weeks, remaining elevated for several months after uncomplicated infections. 1, 3
• ASO testing cannot distinguish active infection from carrier state and reflects only past immunologic events. 2, 3
• A single elevated ASO measurement without clinical context is prone to misinterpretation—serial measurements with anti-DNase B testing are recommended for optimal diagnosis. 4

When Treatment IS Indicated

For Acute Rheumatic Fever (ARF)

If elevated ASO is accompanied by ARF manifestations (migratory arthritis, carditis, chorea, erythema marginatum, subcutaneous nodules), immediate antibiotic treatment is mandatory to prevent permanent cardiac valve damage and mortality. 1

• First-line treatment: Penicillin V 500 mg orally twice or three times daily for 10 days, OR amoxicillin 50 mg/kg once daily for 10 days. 1
• For penicillin-allergic patients: Cephalosporins, clindamycin, or azithromycin (though resistance patterns must be considered). 1
• Treatment duration must always be 10 days—shorter courses increase the risk of acute rheumatic fever. 1
• The primary objective is preventing acute rheumatic fever progression and secondary suppurative complications (peritonsillar abscess, cervical lymphadenitis, mastoiditis). 1

For Post-Streptococcal Glomerulonephritis

• If elevated ASO occurs with hematuria, proteinuria, edema, and hypertension, confirm the diagnosis and treat the streptococcal infection with the same antibiotic regimens as ARF. 1
• Treatment focuses on eradicating residual GAS infection, though the glomerulonephritis itself is typically self-limited. 1

When Treatment Is NOT Indicated

Do not treat an isolated elevated ASO titre without evidence of post-streptococcal complications. 2, 4

• ASO testing is not indicated for diagnosing acute pharyngitis—rapid antigen detection tests or throat culture are appropriate for acute infections. 2
• Elevated ASO can be found in various clinical conditions unrelated to post-streptococcal disease, including many patients with reactive arthritis, non-specific arthralgia/myalgia, or exacerbations of pre-existing rheumatic disease. 2, 5
• In one study, only 14% of patients with elevated ASO had positive streptococcal cultures, and there was no correlation with inflammatory markers (ESR, CRP, RF). 5

Critical Diagnostic Algorithm Before Treatment

1. Confirm the clinical context: Is there evidence of ARF (Jones criteria) or post-streptococcal glomerulonephritis? 1, 2
2. Order anti-DNase B if ASO is negative or equivocal but clinical suspicion remains high—combined testing detects streptococcal infection in up to 98% of proven cases. 2, 3
3. Use age-specific reference ranges—normal ASO levels are significantly higher in school-age children than adults, and misinterpretation is common. 2, 6
4. Consider serial testing—a rising titre is more diagnostically significant than a single elevated value. 4, 7

Common Pitfalls to Avoid

• Do not treat asymptomatic elevated ASO as if it were active streptococcal pharyngitis—this represents past infection, not current disease requiring antibiotics. 2, 4
• Do not order ASO for routine arthritis evaluation—it is not indicated for rheumatoid arthritis (use RF and anti-CCP), seronegative spondyloarthropathies (use imaging), or crystal arthropathies (use joint aspiration). 2
• Do not use low cut-off values in high-burden settings—using globally accepted, age-specific lower serologic cut-offs avoids misclassification, but extremely high cut-offs (as used in some New Zealand protocols) may undercount definite ARF cases. 6
• Do not assume positive culture is required—elevated ASO with appropriate clinical manifestations is sufficient evidence of preceding GAS infection for diagnosing post-streptococcal complications. 1, 5