Sign in →

Test Code LAB1377 Group B Strep (GBS) Screen PCR

Important Note

The standard of care for preventing neonatal (early-onset) GBS disease, updated in 2019, indicates screening of pregnant women at 36 0/7 – 37 6/7 weeks gestation to determine their GBS colonization status.

The CDC published a revised guideline in November 2010, recommending, as an alternative to culture-based testing, that vaginal/rectal specimens could be tested using a nucleic acid amplification test (NAAT) after 18 – 24 hour incubation period in an appropriate enrichment broth medium to enhance the detection of GBS for antepartum specimens.

Performing Lab

Arnot Ogden Medical Center

Ordering Recommendations

Screening for maternal colonization with Streptococcus agalactiae (group B strep) at 36 0/7 to 37 6/7 weeks gestation as a guide for intrapartum antibiotic prophylaxis to decrease the risk of infection by Streptococcus agalactiae in the infant.

IV penicillin remains the preferred agent for intrapartum prophylaxis and is recommended for non-penicillin-allergic women. Additionally, ACOG 2019 guidelines recommend women with non-severe penicillin allergies may be treated with first generation cephalosporins, including cefazolin. Streptococcus agalactiae and other beta-hemolytic strep remain predictably susceptible to penicillin and cefazolin. AST is not therefore necessary for these agents.

Clindamycin is the recommended agent for prophylaxis of women with severe penicillin allergy. Rates of resistance to both erythromycin and clindamycin are increasing with recent studies reporting 15%-40% clindamycin resistant isolates. 

If susceptibility testing of GBS is needed due to a penicillin allergy, please note this in the order.
 

Collect

Culturette Swab Vaginal/Rectal specimen

Stability (from collection to initiation)

Room Temperature 24 hours
Refrigerated 48 hours

 

Storage/Transport Temperature

Room Temp or Refrigerated

Methodology

Real-Time PCR

Start Date

9/13/2017

Last Review Date

6/23/2025

Specimen Handling

Room Temp or Refrigerated

Reference Interval

Not Detected

Approximately 10–30% of pregnant women are colonized with GBS in the vagina or rectum. GBS colonization can be transient, chronic, or intermittent. Culture screening of both the vagina and rectum for GBS late in gestation during prenatal care can identify women who are likely to be colonized with GBS at the time of delivery.

Interpretive Data

LIMITATIONS:

  • Erroneous test results might occur from improper specimen collection, technical error, and sample mix-up. Careful compliance to the instructions in this insert is important to avoid erroneous results.
  • A negative result does not rule out the possibility of GBS colonization. False negative results may occur if the organism is present at levels below the analytical limit of detection.
  • The performance of the Xpert GBS LB CX Assay was validated using the procedures provided in this package insert only. Modifications to these procedures may alter the performance of the test.
  • The Xpert LB XC Assay has been validated with Lim broth medium only. Performance of the assay has not been validated with other GBS selective broth enrichment media.
  • Culture isolates are needed for performing susceptibility testing as recommended for penicillin-allergic women. Use remaining enriched Lim broth to obtain culture isolates.
  • Good laboratory practices should be followed and gloves should be changed between handling each patient specimen in order to avoid contamination of specimens or reagents.
  • Culture test results may be affected by concurrent antibiotic therapy. GBS DNA may continue to be detected following antimicrobial therapy.
  • The effect of interfering substances has only been evaluated for those listed within the package insert. Interference by substances other than those described can lead to erroneous results.
  • A positive result does not necessarily indicate the presence of viable organisms.
  • Mutations or polymorphisms in primer or probe binding regions may affect detection of new or unknown GBS variants and may result in false negative results.

Collection Instructions

  • Wipe away excess amount of secretions or discharge.
  • Remove BBL aerobic swab from transport tube.
  • Insert the swab into the vagina.  Sample secretions from the mucosa of the lower one-third of the vagina.  Rotate the swab three times.
  • Using the same swab, insert approximately 2.5cm beyond the anal sphincter and gently rotate three times.
  • Place swab back into the transport container.

Remarks

Group B Strep Screen is for Vaginal/Rectal swabs only.

Turn Around Time

24 hours

Reported

24 hours