Laboratory: Clinical Microbiology
Test Name:
Antistreptolysin O Titre (ASOT), Serology (HSC Only) - (S)
Test Code: ASOT
Clinical Information:
Test Indications:
In infections caused by Streptococcus pyogenes (Group A Streptococcus), streptolysin O is released by the bacteria stimulating production of antistreptolysin O antibodies.  Detection of antistreptolysin O antibodies is useful in determining whether a patient has had recent infection with S. pyogenes.  In particular, a positive antistreptolysin O titre (ASOT) may be helpful in supporting a diagnosis of immunologically mediated sequelae related to recent S. pyogenes infection.

Testing for antistreptolysin O antibodies is indicated when the diagnosis of poststreptococcal disease is being considered, including the following situations: (1) investigation of rheumatic fever in a patient with clinically compatible symptoms and signs; and (2) investigation of glomerulonephritis.
Note: antibodies against streptolysin O reach a maximum at 3-6 weeks after infection.  Soft tissue infection/pyoderma caused by S. pyogenes does not elicit a strong antistreptolysin-O response.  A negative result does not rule out the diagnosis of acute rheumatic fever or poststreptococcal glomerulonephritis.  When testing for poststreptococcal disease, consideration should also be given to ordering an anti-DNase B titre (offered through Cadham Provincial Laboratory).  Beta-hemolytic streptococci other than S. pyogenes can also produce streptolysin O, so a positive test is not specific for infection due to S. pyogenes.

Patient Preparation Instructions:
Patient preparation should follow the procedure outlined by your healthcare facility.
Accurate patient identification must be made prior to sample collection.  Patient identification should be done in accordance with your healthcare facility's policy.
Samples and requisitions must be labeled/completed in accordance with the DSM Specimen Acceptance Policy.
Collection Devices:
Specimen Required:
Blood: 3.0 mL
Pediatric Blood: 3.0 mL

Cadham Provincial Lab - Guide to Services

Adult: Blood: 3 mL preferred, 1 mL minimum

Pediatric: Blood: 3 mL preferred, 1 mL minimum
Reference Values:
An ASOT of <200 IU/L is considered a normal value (negative test result).
A semiquantative result will be provided for positive samples.  A result of 200 IU/L or greater is considered diagnostically significant.
See Also:
More Information:
Specimen Handling:
Transport to the Clinical Microbiology Laboratory as soon as possible.  If transport will be delayed, store the specimen at 2-8°C.