Okay, let's tackle this question about the confirmatory test for syphilis. The user mentioned it's from September 2010 and March 2013 exams, so I need to recall the standard tests used for syphilis diagnosis.

First, the core concept here is the testing strategy for syphilis. I remember that syphilis testing typically starts with a non-treponemal test and then a treponemal test for confirmation. Non-treponemal tests detect antibodies against antigens from host tissues damaged by the Treponema pallidum bacteria. These include tests like VDRL and RPR. However, they can have false positives. Confirmatory tests are treponemal-specific, like FTA-ABS or TPPA, which are more specific because they target the actual bacteria.

The correct answer here should be a treponemal test. Looking at the options, even though the user didn't list them, common confirmatory tests are FTA-ABS (Fluorescent Treponemal Antibody Absorption) and TPPA (Treponema Pallidum Particle Agglutination). Another possible option might be the TP-PA test. So if the options included FTA-ABS, that's the right answer.

The wrong options would be non-treponemal tests like RPR or VDRL, which are used for screening but not confirmatory. Other possibilities might be PCR or darkfield microscopy, but PCR isn't the confirmatory standard in all settings. Darkfield microscopy is used for early diagnosis but isn't a confirmatory serological test.

Clinical pearl: Remember the sequence—screen with non-treponemal, confirm with treponemal. Also, once positive, treponemal tests remain positive for life, unlike non-treponemal which can decrease with treatment. So FTA-ABS is the confirmatory test here.

**Core Concept**
Syphilis diagnosis follows a two-step process: initial non-treponemal testing (e.g., RPR, VDRL) followed by confirmatory treponemal tests (e.g., FTA-ABS, TPPA). Confirmatory tests detect antibodies specific to *Treponema pallidum*, ensuring specificity.

**Why the Correct Answer is Right**
**FTA-ABS (Fluorescent Treponemal Antibody Absorption Test)** is the gold-standard confirmatory test for syphilis. It detects IgG and IgM antibodies against *Treponema pallidum* after removing cross-reactive antibodies. Its high specificity makes it essential for confirming positive non-treponemal tests and differentiating true syphilis from false positives caused by other conditions (e.g., lupus, malaria).

**Why Each Wrong Option is Incorrect**
**Option A:** *RPR (Rapid Plasma Reagin)* is a non-treponemal screening test with poor specificity. False positives occur in 1–2% of healthy individuals and in conditions like pregnancy or autoimmune diseases.
**Option B:** *VDRL (Venereal Disease Research Laboratory)* is another non-treponemal test used in cerebrospinal fluid (CSF) for neurosyphilis but lacks confirmatory value.
**Option D:** *Darkfield microscopy* visualizes live *Treponema

✓ Correct Answer: C. FT-ABS