title: Repetition of the rapid antigen test in initially negative supposed streptococcal pharyngitis is not necessary in adults.
abstract: OBJECTIVE
  To determine whether the repetition of the rapid antigen detection test (RADT) in patients, with a high suspicion of presenting pharyngitis by group A beta-haemolytic streptococci (GABHS), with a previously negative test improves the validity of the test.
  
  
  METHODS
  Two hundred and twenty-two patients aged 14 years or more with acute pharyngitis and two or more Centor criteria--tonsillar exudates, fever, tenderness in the lymph glands and/or absence of cough--were consecutively recruited. In all patients, a pharyngotonsillar sample was obtained with two swabs, one for the RADT (OSOM Strep A Genzyme test, Genzyme Diagnostics, Cambridge, MA, USA) and the other was sent to the Department of Microbiology for culture. In patients with a negative RADT, the determination was repeated. The sensitivity, specificity and predictive values were determined.
  
  
  RESULTS
  Cultures were positive for GABHS in 55 patients (24.8%). Three false-negatives and 14 false-positives were observed by comparing the rapid test with throat culture, achieving a sensitivity of 94.5% and a specificity of 91.6%. Positive and negative predictive values were 78.8% and 98.1% respectively. Taking the second determination in the negative cases into account, the results were 96.4%, 91.6%, 79.1% and 98.7% respectively.
  
  
  CONCLUSIONS
  The negative predictive value achieved with the RADT determination was very high. Repetition of the test only slightly improved this percentage, making repetition of this test unnecessary.
authors.affiliation: Primary Care Centre Jaume I, University Rovira i Virgili, Tarragona, Spain. carles.llor@urv.cat
authors.forename: C
authors.initials: C
authors.lastname: Llor
authors.forename: O
authors.initials: O
authors.lastname: Calviño
authors.forename: S
authors.initials: S
authors.lastname: Hernández
authors.forename: S
authors.initials: S
authors.lastname: Crispi
authors.forename: M
authors.initials: M
authors.lastname: Pérez-Bauer
authors.forename: Y
authors.initials: Y
authors.lastname: Fernández
authors.forename: T
authors.initials: T
authors.lastname: Martínez
authors.forename: F F
authors.initials: FF
authors.lastname: Gómez
authors.forename: J M
authors.initials: JM
authors.lastname: Cots
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000942:Antigens, Bacterial / Q000032:analysis*; D006801:Humans; D007159:Immunologic Tests / Q000379:methods / Q000592:standards*; D008875:Middle Aged; D010612:Pharyngitis / Q000382:microbiology*; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013290:Streptococcal Infections / Q000175:diagnosis*; D013291:Streptococcus / Q000276:immunology*; D055815:Young Adult
chemical_list: D000942:Antigens, Bacterial