Congenital syphilis laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Kalsang Dolma, M.B.B.S.[2]; Aditya Govindavarjhulla, M.B.B.S. [3]

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Laboratory Findings

• Blood tests
  • Complete blood count
  • Differential count
  • Platelet count
• CSF analysis

Infants delivered of women with a reactive STS should have a cerebrospinal fluid (CSF) evaluation in any of the following circumstances:

• The infant shows any signs compatible with congenital syphilis OR
• Maternal therapy was inadequate, unknown, or it occurred late (greater than or equal to 20 weeks) in pregnancy OR
• Maternal therapy did not include penicillin OR
• Adequate follow-up cannot be ensured

Other living infants with a diagnosis of confirmed or compatible congenital syphilis should have a CSF examination before treatment to provide a baseline for follow-up examination. Although the importance of the CSF examination is debated, a quantitative VDRL CSF test can be meaningful if it is done in conjunction with tests for elevated total protein and lymphocyte count. The RPR card test should not be used for CSF evaluation.

Regardless of CSF results, however, all children with a diagnosis of confirmed or compatible congenital syphilis should be treated with a regimen effective for neurosyphilis.

Serology

The diagnosis of congenital syphilis is complicated by the transplacental transfer of maternal nontreponemal and tre-ponemal IgG antibodies to the fetus. This transfer of antibodies makes the interpretation of reactive serologic tests for syphilis in infants difficult.

All infants born to mothers who have reactive nontreponemal and treponemal test results should be evaluated with a quantitative nontreponemal serologic test (RPR or VDRL) performed on infant serum because umbilical cord blood can become contaminated with maternal blood and could yield a false-positive result. Conducting a treponemal test (i.e., TP-PA or FTA-ABS) on a newborn’s serum is not necessary. No commercially available immunoglobulin (IgM) test can be recommended.

Dark Microscopic Examination

Darkfield microscopic examination or DFA staining of suspicious lesions or body fluids (e.g., nasal discharge) also should be performed.

Standard Tests

• Antibody Screening Tests (nontreponemal)
  • Rapid plasma reagin (RPR)
  • Venereal Disease Research Laboratory (VDRL)
  • Unheated serum reagin (USR)
  • Reagin screen test (RST)

• Antibody Confirmatory Tests (treponemal)
  • Fluorescent treponemal antibody absorption (FTA-ABS)
  • Fluorescent treponemal antibody absorption double staining (FTA-ABS DS)
  • Microhemagglutination assay for antibody to T. pallidum (MHA-TP)
  • Hemagglutination treponemal test for syphilis (HATTS)
  • Bio-enzaBead Test (ELISA)

• Direct Examination of Lesion or Tissue
  • Darkfield microscopy
  • Direct fluorescent antibody test for T. pallidum (DFA-TP)
  • Silver stains (modified Steiner)
  • Hematoxylin and eosin (H & E) stains

Non Standard Tests

• FTA-ABS immunoglobulin (IgM)
• FTA-ABS 19S IgM
• IgM capture ELISA