Streptococcal Pharyngitis

Despite its imperfections, the throat culture remains the "gold standard" against which all rapid streptococcal antigen detection tests are compared. Using triple throat swabs, the accuracy of a rapid latex agglutination (LA) test and back up throat culture was determined and compared with a simultaneously obtained additional throat culture in children with suspected streptococcal pharyngitis. Although there was a 95 percent concordancy between throat cultures, the sensitivity of the throat culture was only 87 percent. Despite the LA test's lower sensitivity (78 percent), in this clinical population with a relatively low prevalence of positive throat cultures (19 percent), the predictive value of a negative LA test was only slightly lower than that of the throat culture (94-95 percent vs. 97 percent). Backup throat cultures are commonly recommended for patients with initially negative LA test results, but 10 percent of the patients with group A beta-hemolytic streptococci-positive throat cultures would have been undetected using this approach.