A 25-year-old male presents with C/O rash. There is no fever or myalgia. A slightly pruritic maculopapular rash is noted over the abdomen, trunk, palms of the hands and soles of the feet. Lymphadenopathy is also noted. Hyperophic, flat, walike lesions are noted around the anal area. Lab studies show: PCV: 40% HB: 14 g/dL WBC: 13,000/ml DLC: N50, L50 The most useful laboratory test in this patient is

**Core Concept**
The patient presents with a maculopapular rash, lymphadenopathy, and specific lesions around the anal area, suggesting a diagnosis of secondary syphilis. The underlying principle being tested is the ability to identify the most useful laboratory test for diagnosing syphilis.

**Why the Correct Answer is Right**
The most useful laboratory test for diagnosing syphilis is the **Venereal Disease Research Laboratory (VDRL) test** or the **Rapid Plasma Reagin (RPR) test**, which are non-treponemal tests. However, the **Treponema Pallidum Haemagglutination (TPHA) test** or **Fluorescent Treponemal Antibody Absorption (FTA-ABS) test** are more specific. These tests detect antibodies against **Treponema pallidum**, the causative agent of syphilis.

**Why Each Wrong Option is Incorrect**
**Option A:** Not specified, but likely a non-specific test.
**Option B:** Not specified, but likely a non-specific test.
**Option D:** Not specified, but likely a non-specific test.

**Clinical Pearl / High-Yield Fact**
The presence of a maculopapular rash on the palms and soles is a classic sign of secondary syphilis. Remember, syphilis is a **"great imitator"** and can present with various symptoms, making laboratory diagnosis crucial.

**Correct Answer:** D. VDRL test

✓ Correct Answer: B. VDRL test