Treponema pallidum cannot be cultured in routine laboratory media. Which serological test combination is recommended for definitive diagnosis of syphilis, distinguishing biological false positives from true syphilis?

• A RPR (screening) + PCR for T. pallidum (confirmatory)
• B VDRL (screening) + FTA-ABS or TPPA (confirmatory treponemal test) ✓
• C Darkfield microscopy alone — the gold standard for all stages
• D TPHA alone — sufficient for both screening and confirmation

Explanation

The traditional algorithm uses non-treponemal tests (VDRL/RPR) for screening and quantifying treatment response; false positives occur with SLE, pregnancy, malaria, tuberculosis. Positive non-treponemal tests must be confirmed with treponemal-specific tests — FTA-ABS (fluorescent treponemal antibody absorption) or TPPA (T. pallidum particle agglutination) — which detect antibodies to T. pallidum antigens and remain positive lifelong. Biological false positives on VDRL are non-reactive on FTA-ABS/TPPA. Darkfield microscopy is useful only for primary syphilis chancre exudate. The reverse algorithm (treponemal first by EIA, then non-treponemal) is now used in many labs.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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