Confirmatory test for syphilis:-
Syphilis testing typically involves both screening and confirmatory tests. The screening tests are usually nontreponemal like VDRL or RPR. Confirmatory tests are treponemal-specific, such as FTA-ABS or TPA. So the correct answer is likely FTA-ABS. If option C is FTA-ABS, then that's the right choice. The other options might be other tests like VDRL (non-treponemal, screening), TP-ELISA (another treponemal but confirmatory), or maybe something else like a rapid test.
Wait, but some sources mention TPHA as another confirmatory test. Need to check if FTA-ABS is the most commonly cited confirmatory test. Also, TPA (Treponema pallidum particle agglutination) is another one. So the correct answer is either FTA-ABS or TPA. But in most textbooks, FTA-ABS is the gold standard for confirmation after a positive nontreponemal test. So I should structure the explanation around that.
**Core Concept**
Confirmatory syphilis tests detect **Treponema pallidum** antigens or antibodies using treponemal-specific assays. Nontreponemal tests like VDRL/RPR are screening tools, while treponemal tests confirm infection via direct antigen detection or IgM/IgG antibody binding.
**Why the Correct Answer is Right**
The **FTA-ABS (Fluorescent Treponemal Antibody Absorption) test** is the gold standard confirmatory test. It detects IgG antibodies against *Treponema pallidum* after absorbing nonspecific cross-reacting antibodies. This high specificity makes it reliable for confirming syphilis post-nontreponemal screening. Other treponemal tests (e.g., TPHA, TPA) are also used but FTA-ABS remains the most sensitive and specific.
**Why Each Wrong Option is Incorrect**
**Option A:** VDRL (Venereal Disease Research Laboratory) is a **nontreponemal test** used for initial screening, not confirmation. False positives occur in conditions like lupus or malaria.
**Option B:** RPR (Rapid Plasma Reagin) is another **nontreponemal test** for screening; it measures reagin antibodies and is not specific to *T. pallidum*.
**Option D:** TP-ELISA (Treponemal Enzyme-Linked Immunosorbent Assay) is a confirmatory test but less specific than FTA-ABS; it detects IgM/IgG antibodies but can cross-react in treated cases.
**Clinical Pearl / High-Yield Fact**
Always follow a **positive nontreponemal test (VDRL/RPR)** with a **treponemal confirmatory test (FTA-ABS)** to avoid false positives. Remember: *"Screen with nontreponemal, confirm with trepon