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Paediatric Laboratory Medicine

Anti-Streptolysin O titer

Clinical Significance

Diagnosis of group A streptococcal infections and their non-supprative complications

Test Name

Anti-Streptolysin O titer

Test Code





Latex agglutination

External Proficiency Testing

College of American Pathologists

Turn Around Time

1x per week


  • Diagnosis of group A streptococcal infections
  • Non-supprative complications of group A streptococcal infection - rheumatic fever and acute post streptococcal glomerulonephritis

Specimen Type


Minimum Specimen Requirements

  • Serum - 1 mL minimum for 1 test, >1 mL recommended for multiple tests.


  • All specimens must be shipped on dry ice
  • Exception: Specimens that will arrive at SickKids within 24 hours from the time of collection can be shipped on ice packs

Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Phone: 416-813-7200
Phone: 1-855-381-3212


Age greater than or equal to  3 years:

  • Positive ≥ 200 IU/mL

Age less than 3 year:

  • Positive ≥ 50  IU/mL
  • if positive specimen titrated up to 1:3200.
  • No single titer is diagnostic, the mean titer in rheumatic fever is >500 IU/mL.
  • ASOT begins to rise about 1 week post-infection,  reaches maximum by 3-5 weeks post-infection and declines over the next 6-8 weeks.
  • It is recommended that acute and convalescent sera(10 - 14 days after onset of illness) be drawn to document acute infection.