What is the treatment for a patient with an elevated Antistreptolysin O (ASO) titre?

Treatment for Elevated Antistreptolysin O (ASO) Titre

An elevated ASO titre alone does not require treatment unless it is associated with acute rheumatic fever (ARF) or other post-streptococcal sequelae, in which case antibiotic therapy with penicillin is the standard treatment. 1

Understanding ASO Titre

An elevated ASO titre indicates a recent Group A Streptococcal (GAS) infection, not necessarily an active infection requiring immediate treatment:

• ASO titres begin to rise approximately 1 week after GAS infection
• Peak between 3-6 weeks post-infection
• May remain elevated for months after the infection has resolved 1, 2

Diagnostic Approach

When evaluating an elevated ASO titre, consider:

1. Clinical correlation: Determine if there are symptoms of post-streptococcal sequelae:

   • Acute rheumatic fever (carditis, arthritis, chorea, erythema marginatum, subcutaneous nodules)
   • Post-streptococcal glomerulonephritis
   • Other inflammatory conditions 1

2. Additional testing:

   • Consider paired ASO titres (acute and convalescent) to demonstrate rising titers
   • Anti-DNase B antibody testing (another streptococcal antibody marker)
   • ESR and CRP to assess inflammation (≥60 mm/h for ESR in low-risk populations)
   • Complete blood count 1, 2

Treatment Algorithm

1. Asymptomatic Elevated ASO Titre

• No treatment required - an isolated elevated ASO titre without clinical manifestations does not require antibiotic therapy 1, 3
• Monitor for development of symptoms

2. Acute Rheumatic Fever with Elevated ASO Titre

• Eradicate residual GAS infection:

  • First-line: Penicillin V orally for 10 days OR benzathine penicillin G as a single intramuscular injection 1, 4
  • For penicillin-allergic patients: Oral macrolide (e.g., azithromycin) 1, 5

• Establish secondary prophylaxis to prevent recurrences:

  • Benzathine penicillin G 1.2 million units IM every 3-4 weeks 1
  • Alternative for penicillin-allergic patients: Oral sulfadiazine or macrolide 1

3. Other Post-Streptococcal Sequelae

• Treat with appropriate antibiotics as per the specific condition
• Anti-inflammatory therapy may be required for symptom management

Special Considerations

• Timing matters: ASO titres can remain elevated for months after an infection has resolved, so treatment decisions should not be based solely on elevated titers 1, 3

• Differential diagnosis: Elevated ASO titers can be found in various clinical conditions other than post-streptococcal diseases and do not necessarily correlate with inflammatory parameters 3

• False positives: Only 14% of patients with elevated ASO have positive streptococcal cultures, indicating that many elevated titers are not related to active infection 3

Common Pitfalls to Avoid

• Overtreatment: Treating based on ASO titers alone without clinical correlation can lead to unnecessary antibiotic use 1

• Inadequate prophylaxis: For confirmed ARF, insufficient duration or frequency of prophylaxis increases the risk of recurrences 1

• Misinterpretation: Elevated ASO indicates recent past infection, not necessarily active infection requiring treatment 1, 2

By following this approach, clinicians can appropriately manage patients with elevated ASO titres while avoiding unnecessary antibiotic use and ensuring proper treatment for those with post-streptococcal sequelae.