In a patient with SLE, which test is most likely to be positive due to antiphospholipid antibodies?

• A. ASO titers
• B. VDRL/RPR
• C. HLA-B27
• D. ANA

Answer: (B)

Antiphospholipid antibodies, especially anticardiolipin antibodies seen in SLE, can cause a false-positive non-treponemal test for syphilis. VDRL and RPR detect reagin antibodies that react with cardiolipin in the test antigen, not with Treponema pallidum. When anticardiolipin antibodies are present, they bind to cardiolipin in these assays and produce a positive result even if the patient does not have syphilis. This is why a positive VDRL or RPR can occur in antiphospholipid syndrome or SLE. If there’s clinical concern for true syphilis, a confirmatory treponemal test (like FTA-ABS or TP-PA) is used, which remains positive only with true treponemal infection. The other options are not driven by antiphospholipid antibodies: ASO titers reflect past streptococcal infection, HLA-B27 is linked to certain rheumatologic conditions, and ANA is a general autoimmune marker in SLE but not specifically tied to antiphospholipid antibodies.