Diagnostic Potential for IgM Antibody Detection by the DPP Syphilis TnT Assay in Neonates at Risk for Congenital Syphilis.

Background: Neonatal IgM antibodies reflect an in-utero immune response to Treponema pallidum and may offer added diagnostic value. This study evaluated the test performance of treponemal IgM levels measured by the research-use-only (RUO) DPP Syphilis TnT point-of-care (POC) assay for CS risk stratification. Methods: Conducted from May 2023 to May 2025, this study tested neonatal serum samples from infants born to mothers with syphilis using the DPP Syphilis TnT RUO POC assay, which reports treponemal and nontreponemal IgM levels as relative light units (RLU). Neonates were classified as Confirmed Proven or Highly Probable CS, Possible CS, or CS Less Likely per guidelines; 23 neonates without maternal syphilis served as controls. Treponemal IgM levels were compared across categories using nonparametric tests and ordinal logistic regression. Diagnostic performance used prespecified cutoffs, with agreement assessed against neonatal RPR. Results: Twenty-two maternal-neonatal dyads were included. Mean treponemal IgM levels rose with CS severity, peaking in the high-risk group (Possible or Confirmed Proven/Highly Probable CS: 29.9 ± 20.6 RLU) versus CS Less Likely (17.5 ± 20.8 RLU) and controls (3.5 ± 0.8 RLU; p<0.05). Higher IgM levels independently linked to elevated CS risk (OR 1.10 per 1 RLU; p=0.0025). At ≥10 RLU cutoff, treponemal IgM detected 88.9% of high-risk neonates, with 76% agreement to neonatal RPR. Conclusion: The DPP Syphilis TnT RUO POC assay's treponemal IgM levels discriminated CS risk categories effectively and may supplement current algorithms to improve neonatal CS stratification.