Performance of Rapid Streptococcal Antigen Testing Varies by Personnel

Abstract

Rapid carbohydrate antigen tests are frequently used to diagnose group A streptococcal (GAS) pharyngitis. Despite evidence of modest sensitivity in medical settings, rapid antigen tests are available to the public for self-testing. We sought to determine if the personnel performing a rapid streptococcal antigen test influence the test's performance characteristics. Throat swabs of pediatric patients performed for GAS pharyngitis in a tertiary-care children's hospital network were included during two study periods in 2004 and 2005. The performance characteristics of a rapid carbohydrate antigen test were evaluated in three clinical settings against a nucleic acid probe test method according to the personnel performing the test (laboratory technologist versus nonlaboratory personnel). Between the study periods, nonlaboratory personnel from one site underwent retraining. Subsequently, the performance characteristics of the rapid antigen test were reassessed. The sensitivity of the rapid antigen test varied widely among the different testing sites (56 to 90%). Notably, test sensitivity was consistently greater when the test was performed by laboratory technologists than when it was performed by nonlaboratory personnel (P < 0.0001). Although the rapid antigen test sensitivity significantly improved after nonlaboratory personnel at one testing site were retrained (sensitivity before versus after retraining; P < 0.0001), the sensitivity remained greater in the laboratory technologist cohort (P < 0.0001). These data confirm the important relationship of the operator performing a rapid streptococcal antigen test with the test's accuracy, even in a clinical setting, where operator training is mandated. Therefore, its use outside the medical setting by lay persons cannot be recommended without culture backup.

STARD 2015 guidelines for reporting diagnostic accuracy studies: explanation and elaboration

“…41 42 The quality of reading has also been shown to be affected in cytology and microbiology by professional background, expertise and prior training to improve interpretation and to reduce interobserver variation. [43][44][45] Information about the amount of training of the persons in the study who read the index test can help readers to judge whether similar results are achievable in their own settings.…”

Guideline for the management of acute sore throat

“…As a result of this bias, often called ‘spectrum bias’, the performance of RAT is not an absolute feature of a given test [37,59]. To improve the accuracy of RAT, the RAT should be performed by trained staff [60] and performed in the posterior pharyngeal wall and both tonsils (Tables 14 and 15; [49,61,62]).…”

In vitro evaluation and comparison of 5 rapid antigen detection tests for the diagnosis of beta-hemolytic group A streptococcal pharyngitis

“…Several RADTs are available in most countries, but sensitivity and specificity performances are variable depending on the RADT (Ruiz-Aragon et al, 2010). Besides these intrinsic performance differences, variations inherent to both the operator and the load of inoculums have been shown in several studies (Cohen et al, , 2013Fox et al, 2006;Hall et al, 2004;Kurtz et al, 2000). A rigorous technical and practical evaluation of such tests, therefore, requires overcoming these interindividual variations using standardized in vitro protocols with known concentrations of GAS.…”