(507) The Use of a Novel Point-Of-Care (POC) IgM Test for the Diagnosis of Congenital Syphilis

The only hematologic test used for congenital syphilis (CS) diagnosis is the neonatal nontreponemal (NT) serologic combined antibody test directed towards T. pallidum antigens. This includes IgG antibodies which cross the placenta and may reflect maternal antibodies rather than neonatal infection. In contrast, any syphilis-specific IgM immunoglobulins detected in the neonate are fetal in origin and may reflect CS. This pilot study aims to determine the test performance of a POC IgM test for the diagnosis of CS.

Study Design:

After institutional review board approval, serum from 2 controls and 23 pregnant patients with syphilis and their newborns was collected between 05/24-06/24. Duplicate 20 µL aliquots were tested using the research-use only rapid lateral flow test developed by Diagnostics Direct, LLC for detection of syphilis IgM. This test uses a purified specific anti-IgM polyclonal antibody coupled with colloidal gold in the sample pad to form rose colored visually read test and control lines.  A proprietary Protein is used to bind all IgG from reacting with the antigen test line, producing only IgM for visual results detection. Duplicate 50 µL aliquots from the samples were tested for IgM using two CE-marked Western Blot (WB) tests with different treponema targets as comparators (ViraBlot, Germany and Euroimun, Germany). Mother-baby dyads were staged for syphilis according to the Centers for Disease Control and Prevention guidelines and were also considered for test performance analytics.

Results:

The positive and negative percent agreement (PPA, NPA) between the POC IgM test and the Virablot WB was 86% and 78% and for Euroimun, PPA and NPA were 80% and 86% respectively (Table 1). Clinical correlates were similar, demonstrating a 90% PPA and a 93.3% NPV between the POC IgM test and syphilis diagnosis for dyads (Table 2).

Conclusion: The syphilis POC IgM test demonstrated excellent test performance when compared to reference WB tests and clinical correlates. Given poor sensitivity of current lab tests for CS, further studies evaluating this POC IgM test for at-risk neonates are warranted.