LABORATORY STEWARDSHIP

RPR false-positivity observed during the current SARS-CoV-2 pandemic
 
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
On December 17, 2021 the U.S. Food and Drug Administration (FDA) issued an alert to clinical laboratory staff and health care providers about false-positive test results for syphilis using a certain test kit and the need to perform confirmatory testing for all positive results. 2
On December 20, 2021 the CDC noted the letter acknowledging the FDA’s alert and reminding the healthcare community of the importance of using both RPR and treponemal antibody assays to differentiate between true infection and false-positive RPR results.

Seeking answers and results as a trusted partner for your practice.

Labcorp offers a suite of guideline-based reflexive testing profiles for screening and diagnosis of syphilis, as well as profiles for tracking treatment efficacy in diagnosed individuals. Utilizing the recommended reflexive algorithms will help rule out biological false-positive results. To learn more about testing options, visit us at https://womenshealth.labcorp.com/providers/womens-health/fundamental-syphilis-prevention.
Learn more about the increasing rates of syphilis RPR false positivity observed during the pandemic.
 
 
 
Sources:
1. U.S. Food and Drug Administration (FDA). Possible False RPR Reactivity with BioPlex 2200 Syphilis Total & RPR Test Kit Following a COVID-19 Vaccine – Letter to Clinical Laboratory Staff and Health Care Providers. https://www.fda.gov/medical-devices/letters-health-care-providers/possible-false-rpr-reactivity-bioplex-2200-syphilis-total-rpr-test-kit-following-covid-19-vaccine. Accessed April 2022.
2. Centers for Disease Control and Prevention (CDC). Partners in Prevention letter. CDC website. https://www.cdc.gov/std/fda-alert-12-20-2021.pdf. Accessed April 2022.