Strept Cultures and Rapid Strept Tests Objective. The American Academy of Pediatrics recommends that all negative rapid diagnostic tests for Streptococcus pyogenes pharyngitis be backed up by culture, which creates a dilemma for clinicians who must make treatment decisions without complete diagnostic information at the time of visit. The use of a follow-up serial rapid antigen test instead of a follow-up culture would provide a more timely result.