Okay, let's tackle this question. The patient is a 23-year-old woman with acute right lower quadrant pain and tenderness at McBurney's point. The question is asking which investigation is best to confirm appendicitis.

First, I need to recall the typical presentation of appendicitis. Classic symptoms include periumbilical pain that localizes to the right lower quadrant, nausea, vomiting, and fever. McBurney's point tenderness is a key physical exam finding. But the question is about the best investigation to confirm the diagnosis.

The options aren't provided here, but common investigations for appendicitis include abdominal ultrasound, CT scan, CBC with WBC count, and maybe even a laparoscopy. Let's think about the pros and cons of each.

In adults, CT scan is considered the gold standard for diagnosing appendicitis because it has high sensitivity and specificity. Ultrasound is often used first in children or pregnant women to avoid radiation, but in adults, especially when the diagnosis is uncertain, a CT is better. A CBC might show elevated WBC, but that's non-specific and can be due to other infections. Laparoscopy is a treatment method and also a diagnostic tool, but it's invasive and not the first-line investigation.

So the correct answer is likely CT scan of the abdomen with contrast. The other options would be incorrect because ultrasound is less sensitive in adults, CBC is non-specific, and laparoscopy is more invasive and typically used when surgery is planned.

I need to make sure the explanation covers why CT is the best choice, the reasons other options are wrong, and a clinical pearl about the use of imaging in different populations.

**Core Concept**
Acute appendicitis is diagnosed based on clinical signs (e.g., McBurney's point tenderness) and imaging. The **CT scan of the abdomen with contrast** is the most sensitive and specific imaging modality in adults due to its ability to visualize appendiceal inflammation, surrounding fat stranding, and complications like abscesses.

**Why the Correct Answer is Right**
CT scan provides high-resolution images of the appendix and surrounding structures. It detects appendiceal diameter >6 mm, wall thickening, periappendiceal fat stranding, and fluid. Contrast enhances visualization of inflamed tissue and helps differentiate appendicitis from other causes of right lower quadrant pain (e.g., ovarian torsion, diverticulitis). It is preferred over ultrasound in adults due to higher diagnostic accuracy and lower false-negative rates.

**Why Each Wrong Option is Incorrect**
**Option A:** *Ultrasound* is less reliable in adults due to bowel gas interference but is first-line in children and pregnant patients.
**Option B:** *White blood cell count (WBC)* is non-specific; elevated WBC occurs in infections, trauma, and inflammation.
**Option C:** *Laparoscopy* is a therapeutic intervention and definitive diagnostic tool but not the initial investigation.

**Clinical Pearl / High-Yield Fact**
In adults, **CT scan with contrast** is the gold standard for diagnosing appendicitis. Avoid relying solely on WBC or physical exam findings—imaging is critical to confirm the diagnosis and assess complications (e.g., perforation).

**Correct Answer: C. CT scan of abdomen with contrast**

✓ Correct Answer: A. CT Scan