The conventional methods used to confirm group A streptococcal infection depend on the isolation and identification of the organism on blood agar plates. These methods usually require 18-24 hours of incubation at 37C. This delay in identifying group A streptococcus has often caused physicians to administer therapy without first knowing the etiological agent. Alternatively, the development of the rapid antigen detection test (RADT) has allowed the identification of group A streptococcal carbohydrate on a throat swab in a matter of minutes.
This prompt, point-of-care test has proven a valuable resource in the office management of patients with pharyngitis. RADT has improved the appropriateness of antibiotic therapy and allowed earlier laboratory, evidence-based treatment of group A -hemolytic streptococcal pharyngitis.
Despite the widespread use and broadly demonstrated accuracy of rapid testing, some controversy remains in the clinical community about the need for agar incubation culture as a confirmatory procedure following a positive RADT and prior to the initiation of antibiotic therapy or as a reassay in those instances when RADT results are negative yet clinical findings support a diagnosis of Strep-A infection. In such instances, the perceived need for dual testing can actually increase the overall cost of diagnosis. On balance, however, RADT appears to have accelerate d accurate diagnosis and treatment and to have lowered costs. Furthermore, research on the validity of rapid strep tests without follow-up throat cultures suggests that there is no difference in the complication rate between patients tested with a rapid test over a throat culture.
Thirty-five CLIA-waived antigen tests that test directly from throat swabs are currently available from 26 different biomedical firms, making this assay the most broadly produced point of care diagnostic kit. Among the most popular RADT products are:
Given the commodity nature of RADT products and their similarity of use and reliability, the purchasing decision largely rests on factors such as established vendor relationships, the purchasers confidence in vendor reliability and quality, cost, and ease of access. Whichever product is ultimately chosen, the use of this assay has become a ubiquitous improvement in the primary care setting and, research findings indicate, has contributed to timely, cost-effective patient care.
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