Lab Test

Strep Screen, Group B

Vaginal, Prenatal, Antepartum, Group B Strep Culture, Culture, Group B Strep, GBS

Test Codes




Specimen Collection Criteria

Collect: Vaginal-rectal specimen as described below.

  • It is recommended to use only one swab to screen for colonization with Group B Streptococcus (GBS) in women.
  • Use this swab to first sample the vaginal introitus and then the anorectum. Place the swab into Amies transport medium.

Physician Office/Draw Specimen Preparation

Maintain swab specimen in Amies transport medium at room temperature (20-26°C or 68-78.8°F).

Preparation for Courier Transport

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

Rejection Criteria

  • Specimens received greater than 48 hours after collection.
  • Swabs on which the specimen appears to have dried.
  • Specimens that are not in bacterial transport medium.


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 48 hours
Frozen (-20°C/-4°F or below): Unacceptable

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


Sunday – Saturday, 24 hours a day.
Results available in 2-3 days.

Reference Range

No Group B Streptococcus recovered.

Test Methodology

LIM broth enriched bacterial culture, real-time PCR; antimicrobial susceptibility testing performed only if GBS is isolated.


The presence of Group B Streptococcus in vaginal-rectal specimens obtained from women during the 36th-37th week of pregnancy has been associated with invasive perinatal disease.

Clinical Utility

This test is used to screen only for the presence of Group B Streptococcus. If the clinician is interested in the identification of any other microorganisms that may be present in a specimen, a genital culture (Culture, Genital) should be ordered.

Clinical Disease

Group B Streptococcus (Streptococcus agalactiae) is a major cause of perinatal bacterial infections. It causes endometritis, amnionitis, and urinary tract infections in parturient women and systemic and focal infections in infants from birth until 3 or more months of age. Two distinct forms of invasive disease occur in neonates. Early-onset disease is often characterized by respiratory distress, apnea, shock, pneumonia, and, occasionally, meningitis, and its onset usually occurs within the first 24 hours of life (range, 0 to 6 days). Late-onset disease, which typically occurs after one week of age (range, 7 days to 3 months), is frequently manifested as occult bacteremia or meningitis; other focal infections, such as osteomyelitis, septic arthritis, and cellulitis, can also occur. Group B Streptococcus also cause infections in adults, particularly the elderly, those with diabetes, malignancy, or other immunocompromising conditions.


Group B Streptococcus (GBS) is a common inhabitant of the gastrointestinal and the genitourinary tracts. Less commonly, it colonizes the pharynx. The colonization rate in pregnant women and newborn infants ranges from 5% to 35%. Colonization during pregnancy is usually constant but may be intermittent. Neonatal GBS disease has an incidence of one to five cases per 1,000 live births; the incidence varies considerably among hospitals. Early-onset disease occurs in approximately one infant per 100 to 200 colonized women.

Incubation Period

The incubation period of early-onset disease is less than 6 days. In late-onset disease the incubation period from GBS acquisition to disease is unknown. Onset usually occurs from 7 days to 3 months of age.


Transmission from mother to infant occurs in utero shorly before delivery or during delivery. After delivery, person-to-person transmission can occur. Although uncommon, GBS can be acquired in the nursery from colonized infants or hospital personnel (probably via hand contamination), or in the community. The risk of early-onset disease is increased in pre-term infants born at less than 37 weeks gestation, in those born after the amniotic membranes have been ruptured for more than 18 hours and in infants born of women with intrapartum fever or chorioamnionitis, multiple births (such as twins), or GBS bacteriuria. Low or absent concentration of type-specific serum antibody also appears to be a predispoing factor. The period of communicability is unknown, but it may extend throughout the duration of colonization or of disease. Infants can remain colonized for several months after birth and after treatment of symptomatic infections.


  1. CDC. 2010. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC.MMWR: Recommendations and Reports. 59(RR11); 1-36.

CPT Codes



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