From the Guidelines
The primary benefit of Anti-Streptolysin O (ASO) testing is its role as a diagnostic tool to detect recent streptococcal infections, particularly in diagnosing post-streptococcal complications like acute rheumatic fever or post-streptococcal glomerulonephritis. ASO testing measures antibodies produced against streptolysin O, a toxin released by streptococcal bacteria, and is valuable when the original strep infection was mild or asymptomatic 1. The test is especially useful because ASO antibody levels typically rise 1-2 weeks after infection and peak at 3-6 weeks, making it useful for retrospective diagnosis.
Key Points About ASO Testing
- ASO testing is not a screening test and should be ordered when there's clinical suspicion of post-streptococcal complications 1.
- The test helps clinicians establish a connection between previous streptococcal infections and current symptoms, guiding appropriate treatment decisions.
- Elevated ASO titers can persist for several months after even uncomplicated GAS infections, and normal levels of these antibodies are higher among school-age children than among adults 1.
- Newer tests using latex agglutination or nephelometric assays have not been well standardized against traditional neutralization assays, which can lead to misinterpretation of results 1.
Clinical Application
In clinical practice, ASO testing should be used judiciously, considering the clinical context and the potential for false positives or negatives. Given its utility in diagnosing post-streptococcal complications, ASO testing plays a critical role in preventing long-term sequelae of streptococcal infections, such as rheumatic heart disease. By accurately diagnosing recent streptococcal infections, clinicians can initiate appropriate treatment, including antibiotics and supportive care, to mitigate the risk of these complications 1.
From the Research
Benefits of Anti-Streptolysin O (ASO)
The benefits of ASO can be understood in the context of its role in diagnosing and managing post-streptococcal diseases. Some key points include:
- ASO is used to diagnose acute and post-streptococcal diseases, such as rheumatic fever and poststreptococcal glomerulonephritis 2, 3.
- A combination of ASO and anti-DNase B is recommended for optimal diagnosis of preceding Group A streptococcal (GAS) infection 3.
- Elevated ASO titers can be found in various clinical conditions other than typical post-streptococcal associated diseases, and may not necessarily be accompanied by positive culture or correlate with inflammatory parameters 4.
- The interpretation of a single ASO test result can be challenging, and the likelihood ratio method may be more useful than the "upper limit of normal" method in certain cases 5.
- ASO tests can be used to detect streptolysin-O antibodies in health and suspected streptococcal infections, with varying upper limits of normal values depending on age 6.
Diagnostic Value of ASO
The diagnostic value of ASO can be summarized as follows:
- ASO alone or in combination with other antibodies is not a reliable marker of acute streptococcal infection 2.
- The combination of ASO and ADNaseB is the most sensitive and specific combination for identifying post-streptococcal disease, with a sensitivity of 95.5% and specificity of 88.6% 2.
- A single ASO measurement may not be sufficient for diagnosis, and at least two sequential ASOT measurements, together with simultaneous assay for anti-DNase B, are recommended 3.
Clinical Applications of ASO
The clinical applications of ASO include:
- Diagnosis of post-streptococcal diseases, such as rheumatic fever and poststreptococcal glomerulonephritis 2, 3.
- Evaluation of patients with rheumatic conditions, such as rheumatoid arthritis and polyarthritis 4, 6.
- Detection of streptolysin-O antibodies in health and suspected streptococcal infections 6.