From the Guidelines
Yes, ASO titers should be obtained in a patient with acute polyarthritis following exposure to strep throat. This test measures antibodies to streptolysin O, a toxin produced by group A Streptococcus, and can help confirm a diagnosis of post-streptococcal reactive arthritis or acute rheumatic fever 1. The test should be ordered promptly, though it's essential to note that ASO titers typically rise 1-2 weeks after the initial streptococcal infection and peak at 3-6 weeks. A single elevated titer (>200 units in adults or >300 units in children) can be suggestive, but paired samples showing a rising titer provide stronger evidence.
Some key points to consider when interpreting ASO titers include:
- The test should be interpreted alongside clinical findings and other laboratory tests such as anti-DNase B, which can increase diagnostic sensitivity 1.
- If post-streptococcal complications are suspected, additional workup including throat culture, complete blood count, C-reactive protein, and erythrocyte sedimentation rate should be considered 1.
- Treatment decisions for the arthritis should not be delayed while awaiting ASO results, as appropriate antibiotic therapy (typically penicillin) should be initiated promptly if active streptococcal infection is suspected 1.
- It's also important to note that ASO titers reflect past and not present immunologic events and are of no value in the diagnosis of acute pharyngitis, but they are valuable for confirming prior streptococcal infections in patients suspected of having acute rheumatic fever or acute glomerulonephritis 1.
In terms of management, the American Heart Association recommends that patients with post-streptococcal reactive arthritis be observed carefully for several months for clinical evidence of carditis, and some experts recommend that these patients receive secondary prophylaxis for up to 1 year after the onset of their symptoms 1. However, the effectiveness of this approach is not well established.
Overall, obtaining ASO titers is a crucial step in the diagnosis and management of patients with acute polyarthritis following exposure to strep throat, and the results should be interpreted in the context of clinical findings and other laboratory tests.
From the Research
Acute Polyarthritis and ASO Titers
- In a patient with acute polyarthritis following exposure to strep throat, obtaining ASO (Antistreptolysin O) titers may be relevant for diagnosis, as studies have shown that patients with post-streptococcal reactive arthritis (PSReA) often have elevated ASO titers 2, 3.
- A study published in the Journal of Internal Medicine found that all patients with PSReA had a significant rise in ASO titers, with a mean maximal ASO of 1305 i.u. mL-1 2.
- Another study published in Mayo Clinic Proceedings found that all patients with PSReA had increased titers of anti-DNase B and antistreptolysin O, confirming recent streptococcal infection 3.
Diagnostic Considerations
- The diagnosis of PSReA should be considered in patients with acute polyarthritis, especially if they have a history of recent strep throat infection 2, 3.
- ASO titers can be used to support the diagnosis of PSReA, but should be interpreted in the context of clinical presentation and other laboratory findings 4, 5.
- A study published in the Journal of Rheumatology found a significant correlation between ASO titer and sacroiliac joint disorder, suggesting that ASO titers may be useful in diagnosing PSReA with sacroiliac joint involvement 5.
Clinical Implications
- Patients with acute polyarthritis and a history of recent strep throat infection should be evaluated for PSReA, and ASO titers should be considered as part of the diagnostic workup 2, 3.
- Elevated ASO titers in patients with monoarticular arthritis should prompt a careful cardiac examination to rule out rheumatic fever 6.