A 28-year-old woman presents with a painless indurated ulcer (chancre) on the labium majorum that spontaneously resolves. Eight weeks later she develops a generalised maculopapular rash involving palms and soles, generalised lymphadenopathy, and condylomata lata. VDRL titre is 1:64. Which treponemal test is most appropriate to confirm the diagnosis and is non-reactive in false-positive VDRL?
- A Treponema pallidum haemagglutination assay (TPHA) or TPPA ✓
- B Rapid plasma reagin (RPR)
- C Monospot test (heterophile antibody test)
- D Dark-ground microscopy of blood
Explanation
VDRL and RPR are non-treponemal (reagin) tests that detect IgG/IgM antibodies against cardiolipin-lecithin-cholesterol antigen; they may be false positive in SLE, malaria, pregnancy, and other conditions. Confirmation requires a specific treponemal test such as TPHA (Treponema pallidum haemagglutination assay) or TPPA (particle agglutination), FTA-ABS, or CLIA. Treponemal tests detect antibodies against T. pallidum antigens and remain positive for life (unlike non-treponemal tests which fall with treatment). RPR is another non-treponemal test. Dark-ground microscopy is used for primary chancre fluid examination, not blood.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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