Back-Up Culture Not Needed for Negative Rapid Strep Test Results
Am Fam Physician. 2015 May 1;91(9):643a-648.
Do negative rapid strep test results need to be confirmed by culture?
Although rheumatic heart disease due to group A streptococcal infection has all but disappeared in wealthy countries (Lancet. 2012;379(9819):953–964), some countries still go to great lengths to test for streptococcal throat infections, including the United States. As a result, we spend more than $8 million per each additional case of rheumatic heart disease prevented (Prev Med. 2002;35(3):250–257). This meta-analysis found that the rapid antigen tests widely in use are highly effective in identifying and excluding strep. The sensitivity of these tests is 86% and specificity is 96%, overall and in children. The authors of this analysis argue that this sensitivity is high enough—and the likelihood of rheumatic heart disease is low enough—to drop the long-held practice of confirming negative antigen test results with culture. Maybe one day we will retire strep testing; until then, maybe we can get rid of cultures. (Level of Evidence = 1a)
The investigators searched Medline and Embase to identify 48 studies that compared rapid antigen tests for group A streptococcus with throat culture, the diagnostic standard. They limited their search to English-language studies, but searched bibliographies of identified studies and previous reviews. Two investigators assessed all studies for quality. Studies were performed throughout the world and used six different testing methods (latex agglutination, enzyme-linked immunosorbent assay, and so forth). Overall, the sensitivity of all rapid antigen tests was 86% (95% confidence interval, 83% to 88%) and specificity was 96% (95% confidence interval, 94% to 97%). Results were similar when limited to studies performed in children. Molecular techniques (DNA probes, polymerase chain reaction methods) were slightly better, although these tests have a turnaround time of one to three hours.
Study design: Meta-analysis (other)
Funding source: Self-funded or unfunded
Setting: Various (meta-analysis)
Reference: Lean WL, Arnup S, Danchin M, Steer AC. Rapid diagnostic tests for group A streptococcal pharyngitis: a meta-analysis. Pediatrics.. 2014; 134( 4): 771– 781.
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