Throat culture remains the criterion standard diagnostic test for GAS pharyngitis. Throat specimens are obtained by swabbing both the tonsils and the posterior pharynx. With an adequate throat swab sample and proper culture method, false-negative results occur in less than 10% of symptomatic patients.
Studies have repeatedly demonstrated that the currently available streptococcal rapid antigen detection tests have a sensitivity of 70-90%. In contrast to their relatively low sensitivity, the specificity of these rapid tests has consistently been 90-100%.
Owing to the high specificity of the rapid diagnostic tests, a positive test result does not require a throat culture confirmation. However, guidelines state that any negative rapid streptococcal test result in a child with a clinical presentation suggestive of streptococcal pharyngitis should be followed by a throat culture. Obtaining a culture sample at the same time the rapid test is administered allows for easier confirmation of infection status.
Furthermore, if the clinician believes that the signs and symptoms of an illness collectively point toward a viral etiology, testing is not explicitly recommended. Children diagnosed with a viral illness should not be prescribed antibiotics.
For more information about the work-up of suspected GAS pharyngitis, read here.
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