**Core Concept**
The confirmatory test for syphilis is a specific antibody test that detects treponemal antibodies, which are highly specific for *Treponema pallidum*. Among available tests, FTA-ABS (Fluorescent Treponemal Antibody Absorption) is a treponemal antigen-based test used to confirm syphilis infection.

**Why the Correct Answer is Right**
FTA-ABS detects antibodies against *Treponema pallidum* in serum or cerebrospinal fluid. It is a **treponemal test** that remains positive throughout the course of infection and is highly specific. Unlike non-treponemal tests (like VDRL), it does not cross-react with other diseases and is used as a **confirmatory test** after a positive non-treponemal test. It is widely used in clinical settings for definitive diagnosis.

**Why Each Wrong Option is Incorrect**
Option B: VDRL is a **non-treponemal** test used for screening, not confirmation. It can be positive in other conditions (e.g., lupus, malignancy), and lacks specificity.
Option C: PCR is not routinely used for syphilis diagnosis due to low sensitivity in early stages and difficulty in detecting the organism in clinical samples.
Option D: Culture and sensitivity are not practical for syphilis due to slow growth of *Treponema pallidum* and lack of standardized culture media.

**Clinical Pearl / High-Yield Fact**
Always follow a two-step approach: first screen with **VDRL**, then confirm with a **treponemal test** like FTA-ABS or TPPA. A positive VDRL without a positive treponemal test is not diagnostic of syphilis.

✓ Correct Answer: A. FTA-ABS