Increasing rates of biologic false-positivity have been observed with syphilis RPR assays performed in different labs and with reagents from different manufacturers.
Internal studies at Labcorp, as well as studies performed by others,
suggest that this increased biological false-positivity rate correlates with increasing SARS-CoV-2 antibody prevalence in the U.S. population as a result of viral spread and mass vaccination efforts. It is not clear at this point if the increased biological false-positivity rates are due to interferences from prior natural infection and/or vaccination. The U.S. Centers for Disease Control and Prevention (CDC) letter noted that biological false-positive RPR test results have historically been observed in individuals with autoimmune disorders, systemic infections related to syphilis (e.g. tuberculosis, rickettsial diseases, HIV and endocarditis), as well as following immunization (particularly for smallpox) and during pregnancy.1