A patient is tested for syphilis: VDRL is reactive at 1:64, TPHA is reactive, and FTA-ABS is reactive. After treatment with benzathine penicillin, which serological test best monitors treatment response?

• A FTA-ABS (fluorescent treponemal antibody absorption test)
• B VDRL or RPR quantitative titre (non-treponemal test) ✓
• C TPHA (Treponema pallidum haemagglutination assay)
• D Western blot for Treponema pallidum 15 kDa and 47 kDa antigens

Explanation

Non-treponemal tests (VDRL, RPR) measure anti-lipoidal IgM/IgG antibodies that decline after successful treatment, becoming non-reactive in early syphilis or showing fourfold titre reduction in late stages. They are used to monitor treatment adequacy. Treponemal tests (TPHA, FTA-ABS) become positive early but remain reactive for life even after cure ('serofast') due to persistent treponemal antibodies, so they cannot be used to gauge treatment success. A fourfold decline in VDRL/RPR titre after 6 months indicates adequate response.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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