From the Guidelines
The ASO titer is a valuable tool in diagnosing post-streptococcal complications, but it is not recommended for routine diagnosis of acute pharyngitis as it reflects past, not current, events 1. When interpreting ASO titers, it's essential to consider the clinical context and other laboratory findings.
- Normal ASO titers are typically less than 200 units in adults and less than 100 units in children.
- Elevated levels suggest a recent strep infection, with titers usually rising 1-3 weeks after infection and potentially remaining elevated for several months.
- The test is particularly valuable when diagnosing conditions that develop after strep infections, such as rheumatic fever or glomerulonephritis.
- Serial measurements showing rising titers provide stronger evidence of recent infection, as a single elevated result is not definitive.
- It's crucial to note that some individuals may have naturally high levels without infection, while others might not develop elevated titers despite having had a streptococcal infection. In the diagnosis of acute pharyngitis, throat culture and rapid antigen detection test (RADT) are recommended, as they provide more accurate and timely results 1.
- In children and adolescents, negative RADT tests should be backed up by a throat culture.
- Positive RADTs do not necessitate a back-up culture because they are highly specific.
- Routine use of back-up throat cultures for those with a negative RADT is not necessary for adults in usual circumstances.
From the Research
ASO Titer Overview
- The ASO titer is a serologic test used to detect prior infection by Streptococcus pyogenes 2
- Clinicians often request this test to aid in the diagnosis of conditions such as acute rheumatic fever or post-streptococcal glomerulonephritis 2
Interpretation of ASO Titer Results
- The interpretation of ASO titer results can be challenging and should consider various factors, including:
- Clinical features
- Epidemiological setting
- Pre-test probability
- Specific aspects of the assay 2
Recommendations for Use and Interpretation
- A review of streptococcal serologic assays provides recommendations for their use and interpretation, taking into account the complexities of test results 2