From the Guidelines
The anti-streptolysin O (ASO) test is a valuable tool in diagnosing post-streptococcal complications, with elevated titers indicating a recent group A Streptococcus infection, and should be interpreted alongside clinical symptoms and other laboratory findings 1. When interpreting ASO results, it's essential to consider the timing of the infection, as titers typically rise 1-2 weeks after infection and peak at 3-6 weeks 1.
- Normal ASO titers are typically less than 200 units in adults and less than 100 units in children.
- Elevated levels suggest a recent streptococcal infection.
- A single elevated result isn't always diagnostic; paired samples showing a rising titer provide stronger evidence of recent infection.
- False positives can occur with other conditions like liver disease or tuberculosis. The ASO test is particularly useful in patients with possible nonsuppurative complications of GAS infections, such as acute rheumatic fever or acute glomerulonephritis 1.
- The test requires a simple blood draw and doesn't need special preparation.
- ASO levels should be interpreted alongside clinical symptoms and other laboratory findings, as 20% of patients with streptococcal infections may not develop elevated ASO levels.
- This test helps guide treatment decisions, particularly regarding antibiotic therapy for streptococcal infections and their complications, with recommended treatment schedules including penicillin V, amoxicillin, and benzathine penicillin G for the prevention of rheumatic fever 1.
From the Research
Anti-Streptolysin O Antibodies
- Anti-streptolysin O (ASO) antibodies are measured in the routine evaluation of patients with rheumatic conditions 2
- Elevated ASO titers can be found in various clinical conditions other than the typical post-streptococcal associated diseases, and are not necessarily accompanied by positive culture or correlated with inflammatory parameters 2
- The combination of ASO and anti-deoxyribonuclease B (ADNaseB) is the most sensitive and specific combination for identifying post-streptococcal disease, with a sensitivity of 95.5% and specificity of 88.6% 3
Clinical-Diagnostic Role
- The clinical relevance of ASO is restricted to pediatrics, where it contributes to fulfilling the diagnosis of acute rheumatic fever (ARF) as per Jones criteria 4
- Little or no scientific evidence was found for the use of ASO in patients with pharyngitis, post-streptococcal glomerulonephritis, and in adults with rheumatoid arthritis 4
- The standardization of current automated ASO-latex assays is limited, and attention should be paid to inaccurate reference values and many circumstances causing false positive and false negative results 4
Methodology
- A method for validating a new assay for immuno-nephelometric determination of group streptococcal anti-streptolysin O titres (ASOT) from dried blood spots has been developed 5
- This method is a subcomponent of the penicillin pharmacokinetic studies in children receiving secondary prophylaxis with intramuscular benzathine penicillin for acute rheumatic fever 5