Group B streptococcal infection laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rim Halaby, M.D. [2]
Overview
Any newborn with signs of sepsis should receive a full diagnostic evaluation and receive antibiotic therapy pending the results of the evaluation, regardless of the maternal Group B Streptococcus (GBS) colonization status. Well-appearing newborns whose mothers had suspected chorioamnionitis should undergo a limited diagnostic evaluation and receive antibiotic therapy pending culture results. No routine diagnostic testing for GBS is recommended among well-looking infants unless either the gestational age is <37 weeks or the duration of membrane rupture before delivery was ≥18 hours.[1] The diagnosis of GBS infection is confirmed by the isolation of the organism in either the blood or the cerebrospinal fluid (CSF).
Laboratory Tests
Shown below is a table that summarizes the laboratory tests that are recommended in different scenarios of suspected early-onset GBS infection in neonates.[1]
| Scenario | Recommended Diagnostic Evaluation |
| Infants with signs of sepsis | Complete diagnostic evaluation (class A, level of evidence II)
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| Infants born to women with chorioamnionitis | Limited diagnostic evaluation (class A, level of evidence II)
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| Well-appearing infants PLUS The mother had no chorioamnionitis and no indication for GBS prophylaxis |
No routine diagnostic testing |
| Well-appearing infants PLUS The mother received adequate intrapartum GBS prophylaxis |
No routine diagnostic testing (class B, level of evidence III) |
| Well-appearing infants PLUS The mother had an indication for GBS prophylaxis but received no or inadequate prophylaxis PLUS The infant is well-appearing PLUS Gestational age ≥37 weeks PLUS The duration of membrane rupture before delivery was <18 hours |
No routine diagnostic testing (class B, level of evidence III) |
| Well-appearing infants PLUS Either gestational age <37 weeks OR The duration of membrane rupture before delivery was ≥18 hours |
Limited diagnostic evaluation (class B, level of evidence III)
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In addition to the previous tests, the evaluation of suspected late-onset GBS sepsis requires the analysis of urine specimen collected by either catheterization or suprapubic aspiration.
Laboratory Findings
The diagnosis of GBS infection is confirmed by the isolation of the organism in either the blood or CSF. Blood cultures can be sterile in as many as 15% to 33% of newborns with meningitis.[1]
Other laboratory findings that are indicative of an infection but non-specific to GBS include elevated WBC and abnormal findings in the CSF analysis. Thrombocytopenia might occur in the case of sepsis.