Evaluation of the nontreponemal IgM antibodies in syphilis serofast patients: A new serologic marker for active syphilis.

Background: Serofast status is challenging to interpret in clinical work, and distinguishing active syphilis in serofast patients can provide a reference for clinical diagnosis and treatment. However, effective serologic markers for active syphilis are still lacking.

Objectives: We aimed to explore the possibility of nontreponemal IgM antibodies in distinguishing active syphilis in serofast patients.

Methods: A total of 1501 clinical serum samples were collected from 301 serofast patients, and nontreponemal IgM antibodies were detected by chemiluminescence immunoassay.

Results: The results showed that a total of 29 samples (9.63%) of 301 serofast patients were positive for nontreponemal IgM antibodies, and our limited follow-up data showed that 66.67% (2/3) of the serofast patients progressed to neurosyphilis and cardiovascular syphilis.

Conclusion: These findings demonstrate that most serofast patients with positive nontreponemal IgM antibodies have evidence of progressive syphilis, and nontreponemal IgM antibodies can be used as a new serologic marker for the activity of syphilis. Nontreponemal IgM antibodies may play a role in the management of serofast patients.