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Strep Group A Antigen
Test CodeQSTRP
Alias/See Also
Rapid Strep, OSOM Strep A, GAS Ag, Group A Streptococcus Antigen Assay
Includes
Source, Strep Group A Antigen
Preferred Specimen
1 swab for antigen only. 2 swabs for antigen and culture.
Instructions
Use a sterile culture swab to sample the back of the throat (posterior pharynx), tonsillar crypts, and between the tonsillar pillars and uvula.
Avoid touching the lips, cheeks, tongue, and uvula.
Do not use a collection system containing charcoal or semisolid (gel) transport media.
Deliver to the laboratory promptly.
Note: Throat specimens should not be collected if the patient may have epiglottitis, a rapidly progressing cellulitis with potential to cause complete airway obstruction. Epiglottitis is typically caused by H. influenzae type b, but occasionally by S. aureus or S. pneumoniae. Epiglottitis should be considered in a febrile patient who has a severe sore throat, dysphagia, high-pitched breathing noises or progressive respiratory distress, and minimal findings on visualization of the oropharynx. If epiglottitis is suspected, prompt otolaryngologic consultation for airway management is suggested.
Avoid touching the lips, cheeks, tongue, and uvula.
Do not use a collection system containing charcoal or semisolid (gel) transport media.
Deliver to the laboratory promptly.
Note: Throat specimens should not be collected if the patient may have epiglottitis, a rapidly progressing cellulitis with potential to cause complete airway obstruction. Epiglottitis is typically caused by H. influenzae type b, but occasionally by S. aureus or S. pneumoniae. Epiglottitis should be considered in a febrile patient who has a severe sore throat, dysphagia, high-pitched breathing noises or progressive respiratory distress, and minimal findings on visualization of the oropharynx. If epiglottitis is suspected, prompt otolaryngologic consultation for airway management is suggested.
Transport Container
A rayon swab in liquid bacterial transport medium (Amies or modified Stuart’s medium). Dry swab is also acceptable
Specimen Stability
Room temperature or Refrigerated:
- Dry Swab: 24 hours
- Swab in tranpsort media: 2 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Specimens collected from sources other than the throat or nasopharynx;
Swabs with wooden shafts, calcium alginate, or cotton tips;
Specimens in expired transport devices, or in viral transport medium; and specimens >48 hrs old are unacceptable.
Swabs with wooden shafts, calcium alginate, or cotton tips;
Specimens in expired transport devices, or in viral transport medium; and specimens >48 hrs old are unacceptable.
Methodology
Immunochromatography
Limitations
This test does not differentiate between carriers and acute infection. Organisms other than Group A Streptococcus may cause pharyngitis. This test does not differentiate between viable and nonviable Group A Streptococci. This test should be used only with throat swabs. The use of swab specimens taken from the other sites or the use of other samples such as saliva, sputum or urine has not been established.
Reference Range
Not detected
Clinical Significance
Group A Streptococcus (S. pyogenes) is the most common cause of bacterial pharyngitis (“Strep throat”) causing local pharyngeal pain, adenopathy, and fever. In addition, it is important to treat infections caused by this virulent organism in order to avoid potential, morbid complications including peritonsillar and retropharyngeal abscesses, bacteremia, rheumatic fever, and acute glomerulonephritis. Group A Streptococcus, however, may also be isolated in small numbers as part of the oropharyngeal flora of asymptomatic carriers.
