How is GAS infection diagnosed
What specific laboratory tests are used to confirm a recent GAS infection? Why are they important to get?
About 33% of patients with ARF do not remember having any illness (e.g., pharyngitis) prior to developing symptoms of ARF. Therefore, establishing evidence of a recent GAS infection is critical. Evidence for an infection may be shown through a positive throat culture for GAS or a positive rapid streptococcal antigen test, although only 25% of ARF patients will have one of these positive due to the latent period (average, 18 days; range, 1–4 weeks) between infection and development of ARF symptoms. Additionally, neither test distinguishes between a carrier state and active infection. Therefore, the most useful tests to support a recent GAS infection and diagnosis of ARF are antibodies directed against extracellular products found in the supernatant broth of streptococcal cultures, including the antistreptolysin-O (ASO), antideoxyribonuclease-B (antiDNase-B or ADB), antistreptokinase, antihyaluronidase, and anti-NADase (anti-DPNase). The most commonly used serologies are the ASO and ADB.
