Overview
ASO quantifies antibodies to streptolysin O, a streptococcal exotoxin, reflecting recent group A streptococcal infection.
Clinical Importance
Support diagnosis of post-streptococcal sequelae (e.g., acute rheumatic fever, post-streptococcal glomerulonephritis pathways)
Document preceding streptococcal infection when cultures are negative
Specimen Requirements
- Specimen: serum (preferred for most serology/autoimmune immunoassays) or plasma when the method is validated
- Tube: gold/SST (serum separator) or red-top serum; follow method-specific plasma acceptability
- Handling: allow SST to clot fully; centrifuge and separate promptly; avoid repeated freeze–thaw
- Storage: refrigerate short-term; freeze aliquots for delayed testing per manufacturer stability
- Stability: analyte- and kit-specific; do not exceed validated time/temperature limits
Analytical Method
Nephelometry/immunoturbidimetry or classic titration measures ASO in IU/mL. Serial titers 2–4 weeks apart may demonstrate rise.
Instruments Used
Automated analyzers
- Roche Cobas immunoassay systems
- Abbott Alinity / Architect immunoassay systems
- Siemens Healthineers Atellica / ADVIA Centaur immunoassay systems
- Beckman Coulter Access / DxI immunoassay systems
- bioMérieux VIDAS / BioFire immunoassays (selected analytes)
- Ortho Clinical Diagnostics Vitros immunoassay systems
- DiaSorin LIAISON immunoassay systems
- Phadia / Thermo Fisher ImmunoCAP allergy systems
- Manual ELISA, CLIA, and immunofluorescence platforms
Manual methods
- Manual ELISA, agglutination, and immunofluorescence methods in selected settings
Reference Values
Assay cutoffs, units, and reference intervals are method- and manufacturer-specific. Always interpret against the performing laboratory report (CLSI EP28-A3c for quantitative intervals where applicable). Serologic patterns require clinical correlation and current guideline algorithms (WHO/CDC/society guidance as adopted locally).
Upper reference limits are age- and method-specific (often higher in children). Many adult cutoffs are discussed around <200 IU/mL; use the report interval.
Interpretation
Common Causes of Increased Results
- Elevated ASO; supports recent streptococcal infection; correlate clinically
Common Causes of Decreased Results
- Normal ASO; does not exclude streptococcal disease (timing; skin infections may raise anti-DNase B more than ASO)
Clinical Significance
- Post-streptococcal disease evaluation
Factors Affecting Results
Pre-analytical
- Hemolysis, lipemia, or icterus (assay-dependent interference)
- Wrong tube type or incomplete clotting of SST
- Repeated freeze–thaw of serum aliquots
- Testing too early or too late relative to infection/vaccination timing for serology
Analytical
- Calibration/QC failure; reagent lot shifts
- Hook effect / antigen excess on selected immunoassays
- Heterophile antibodies, rheumatoid factor, or biotin interference (assay-dependent)
Post-analytical
- Applying another laboratory’s cutoff to a different method
- Interpreting a single serology result without clinical timing and confirmatory algorithms
Advantages and Limitations
Advantages
- Useful when throat culture window has passed
Limitations
- Not for diagnosing acute pharyngitis
- Anti-DNase B may be needed for skin-associated sequelae
Clinical Pearls
ASO is a history book of weeks past; it will not catch today’s sore throat.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods (verify current edition). Chapters on clinical immunology and serology.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (verify current edition). Immunoassay and protein chapters.
CLSI and Professional Guidelines
- Centers for Disease Control and Prevention. Laboratory testing recommendations for infectious disease serology and related algorithms (verify current CDC guidance for the pathogen).
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory. CLSI document EP28-A3c (verify current edition).
- Clinical and Laboratory Standards Institute. Immunoassay and related method evaluation documents (e.g., EP05, EP06, EP07, EP17; verify current editions relevant to the assay).
- College of American Pathologists. Accreditation and proficiency testing expectations for immunology/serology (verify current CAP checklist requirements).
- International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). Recommendations relevant to protein and immunoassay measurands (verify current IFCC documents).
WHO Publications
- World Health Organization. Laboratory and diagnostic guidance for serologic and immunologic testing (verify current WHO publication for the analyte/assay).
Frequently Asked Questions
Common questions about using this ASO laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the ASO laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of ASO. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find ASO specimen requirements?
See the Specimen Requirements section on this page for specimen information related to ASO. Confirm collection details against your laboratory protocol.
Where are ASO reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret ASO results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for ASO?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from ASO?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading ASO?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Immunology & Serology topic.
What are the clinical pearls for ASO?
See the Clinical Pearls section for concise laboratory practice notes associated with ASO. Apply pearls alongside institutional protocols.
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