Lab Test

Group A Strep by Nucleic Acid Amplification (with or without Susceptibility)

GAS, Streptococcus, Throat, Pharynx, Pharyngitis, Rectal, Perirectal

Test Codes

Group A Strep by NAA without Susceptibility: EPIC: LAB6907, SOFT: SSA
Group A Strep by NAA with Susceptibility: EPIC: LAB6908, SOFT: SSAS


This test can be ordered with or without susceptibility testing. In general, susceptibility testing should be reserved for patients who are allergic to penicillin.

Specimen Collection Criteria

Collect: ESwab specimen collected from the posterior pharynx/tonsillar region, or perianal cellulitis, and placed in Liquid Amies ESwab (white top) transport system.

Physician Office/Draw Specimen Preparation

Maintain specimen in ESwab transport system at room temperature (20-26°C or 68-78.8°F) prior to transport.

Preparation for Courier Transport

Transport: Swab in ESwab transport system, at room temperature (20-26°C or 68-78.8°F).

Rejection Criteria

  • Frozen specimens.
  • Specimens received in Amies transport media with charcoal or Amies gel transport media.
  • Specimens received in viral transport media (UVT, UTM, M4-RT, etc.).


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 7 days*
Refrigerated (2-8°C or 36-46°F): 7 days*
Frozen (-20°C/-4°F or below): Unacceptable

*When antimicrobial susceptibility testing is needed, the sample should be received in the Laboratory within 24 hours.

Specimen Storage in Department Prior to Disposal:

Room Temperature (20-26°C or 68-78.8°F): 7 days


Dearborn Microbiology Laboratory
Taylor, Trenton and Wayne sent to Dearborn Microbiology Laboratory for testing.

Royal Oak Molecular Pathology Laboratory
Farmington Hills, Grosse Pointe, and Troy sent to Royal Oak Molecular Pathology Laboratory for testing.


Sunday – Saturday
Nucleic Acid Amplification available within 24-48 hours.
Susceptibility results, if requested available within 48-72 hours. 

Reference Range

  • No Group A Streptococcus detected for throat, pharyngeal, rectal, and perirectal sources.
  • No Group C/G Streptococcus detected for throat and pharyngeal sources.

Test Methodology

Nucleic Acid Amplification (FDA-approved). When ordered, antimicrobial susceptibility testing will only be performed for Group A Streptococcus (GAS). Antimicrobial susceptibility testing is NOT available for Group C/G Streptococcus.


This test detects and differentiates Streptococcus pyogenes (GAS) and pyogenic Group C/G Streptococcus from throat/pharyngeal specimens and only Streptococcus pyogenes (GAS) from rectal/perirectal specimens.

Clinical Utility

Streptococci cause a myriad of diseases in humans, including pharyngitis (Strep throat) and skin infections (impetigo, necrotizing fasciitis, toxic shock syndrome). Group A Streptococcus (S. pyogenes) is most commonly implicated and its prompt identification aids in appropriate antimicrobial therapy, thereby greatly decreasing the risk of multi-system sequelae (i.e. rheumatic fever, glomerulonephritis). Certain types of Lancefield Group C and Group C Streptococcus are commonly implicated in acute pharyngitis; these are deemed large colony variants or pyogenic Group C and Group G Streptococcus (S. equi, S. dysgalactiae, S. equisimilis, S. zooepidemicus). Non-pyogenic Group C and Group G Streptococcus or small colony variants are currently known as Anginosus group Streptococcus (formerly S. milleri group) and are rarely implicated in acute pharyngitis.


Streptococcal pharyngitis occurs year-round in temperate climates, but the incidence peaks in the winter and spring months. Infections can occur in any age group but most cases occur among school-age children.

Incubation Period

The incubation period of streptococcal pharyngitis is 2 to 5 days. For impetigo, a 7 to 10-day period between the acquisition of Group A Streptococcus on healthy skin and the development of lesions has been demonstrated.


Streptococcal infections are spread from person to person via inhalation of S. pyogenes laden respiratory droplets. Foodborne and milkborne transmission has also been described. A number of individuals, particularly school-age children, carry S. pyogenes without signs of illness. Carriers are culture positive and seronegative.


  1. Kaplan, E.L., Gerber, M.A., 2009 Group A, Group C, and Group G Beta-Hemolytic Streptococcal Infections. Feigen & Cherry's Textbook of Pediatric Infectious Disease, 6th Edition, Chapter 93, pp: 1225-1239. Saunders Elsevier.
  2. Campos, J., 2010. Group A Streptococcus Culture and Non Culture Tests. Clinical Microbiology Procedures Handbook. 3rd edition. L.S. Garcia, Editor-In-Chief, ASM Press. Washington, D.C. pg. 3.11.8.

CPT Codes

87651, 87184 (only if S. pyogenes susceptibility testing is requested).


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