Treponema pallidum causes syphilis. The FTA-ABS (fluorescent treponemal antibody absorbed) test detects antibodies against treponemal-specific antigens. Which statement about FTA-ABS is most accurate?

• A FTA-ABS becomes positive later than VDRL and is used to confirm a positive VDRL; it reverts to negative with adequate treatment
• B FTA-ABS uses Treponema pallidum (Nichols strain) as antigen, patient serum is pre-absorbed with non-pathogenic treponemal antigens to remove cross-reactive antibodies; it remains positive for life even after treatment ✓
• C FTA-ABS measures IgM anti-cardiolipin antibodies, making it useful for monitoring treatment response in primary syphilis
• D FTA-ABS is the preferred test for diagnosis of neurosyphilis via CSF analysis

Explanation

The FTA-ABS is a specific treponemal test using the Nichols strain of T. pallidum as antigen; patient serum is pre-absorbed with Reiter's treponeme (non-pathogenic) to remove non-specific treponemal antibodies, thus increasing specificity. It is one of the most sensitive and specific treponemal tests (sensitivity >99% in secondary syphilis), becomes positive earlier than VDRL in primary syphilis, and importantly, remains reactive for life after infection regardless of treatment — making it unsuitable for monitoring treatment response. VDRL (non-treponemal, measuring anti-cardiolipin IgM/IgG) is used for treatment monitoring. CSF VDRL (not FTA-ABS) is preferred for neurosyphilis diagnosis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.