In the office laboratory of our private practice, the sensitivity of a single rapid antigen detection (RAD) test for group A streptococci (compared with backup throat culture) was examined over 3 winter periods. When cultures were held only 24 hours, the sensitivity was 92%; in the second period, when cultures were held to 48 hours, the sensitivity declined significantly to 86%; when the cultures were read without knowledge of the RAD test result, the sensitivity was 85%. As the Red Book Committee has suggested, physician office laboratories should validate the sensitivity of their RAD test against culture onto blood agar before abandoning the backup throat culture.

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