Repetition of the rapid antigen test in initially negative supposed streptococcal pharyngitis is not necessary in adults.
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.
Llor
C
C
Primary Care Centre Jaume I, University Rovira i Virgili, Tarragona, Spain. carles.llor@urv.cat
Calviño
O
O
Hernández
S
S
Crispi
S
S
Pérez-Bauer
M
M
Fernández
Y
Y
Martínez
T
T
Gómez
F F
FF
Cots
J M
JM
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
D000942:Antigens, Bacterial