Antistreptolysin O

Detects prior infection with or exposure to Streptococcus pyogenes
Used most often for diagnosis of acute rheumatic fever, and far less useful for streptococcal pharyngitis and post-streptococcal glomerulonephritis
Starts increasing around 1 week after infection, peaking at 3 to 6 weeks, then decreasing thereafter
- Rate of decrease is not related to clinical course
False negatives:
- Sample collected during latency period
- Sample collected late in convalescence
- Post-pyoderma (e.g. post-streptococcal glomerulonephritis)
- Corticosteroids and other immunosuppression
- Early administration of antibiotics
False positives:
- Infection with Group C and Group G streptococci
- Lipemic sample
- Bacterial contamination of sample
- Non-specific normal antibodies
- Tuberculosis
- Active viral hepatitis
- Monoclonal gammopathy

Further Reading