A 30-year-old woman screened antenatally has an RPR reactive at 1:4. Her TPPA and FTA-ABS are both non-reactive, and she is asymptomatic. She reports a history of systemic lupus erythematosus on hydroxychloroquine. This pattern is best explained by:
- A Biological false positive reactivity due to autoimmune disease ✓
- B Prozone phenomenon masking the treponemal tests
- C Early primary syphilis before treponemal antibody development
- D Laboratory error requiring repeat sampling only
Explanation
Non-treponemal tests detect reagin antibodies against cardiolipin-lecithin-cholesterol antigens. These cross-reacting antibodies occur in SLE, antiphospholipid syndrome, malaria, leprosy, pregnancy, IV drug use, and after vaccination, producing a biological false positive: a reactive RPR or VDRL with negative confirmatory treponemal tests. Prozone affects the non-treponemal test itself through antibody excess, not selectively sparing treponemal assays. In pregnancy, a BFP still warrants repeat testing and follow-up to exclude very early disease, but the serologic pattern here is classic for SLE-related false reactivity.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.