Effectiveness of rapid antigen test with throat gargle in detecting group A beta-hemolytic streptococci

OBJECTIVES: The most important disadvantage of rapid antigen tests (RAT) is low sensitivity for the diagnosis of group A beta-hemolytic streptococci (BHS). We determined the sensitivity, specificity, positive and negative predictive values of RAT in gargling samples. PATIENTS AND METHODS: The study included 106 patients (53 females, 53 males, mean age 22+/-12 years; range 16-65 years) with an initial diagnosis of tonsillopharyngitis. Swab samples were taken from the posterior pharyngeal wall and tonsil surface with a sterile cotton swab. Then, gargle samples were obtained by gargling for 10 seconds with sterile 0.9% NaCl to be examined by the RAT for group A BHS. Throat cultures were processed using standard microbiologic techniques. RESULTS: Throat cultures were positive in 12 patients (11.3%) and negative in 94 patients (88.6%). Rapid antigen test yielded five positive (4.7%) and 101 negative (95.2%) results. The sensitivity and specificity rates of RAT with throat gargling were 41.7% and 100%, with positive and negative predictive values of 100% and 93.1%, respectively. CONCLUSION: Despite satisfactory specificity, positive and negative predictive rates of RAT with throat gargling, its low sensitivity limits its use for the diagnosis of group A BHS.