## **Core Concept**
The clinical presentation described suggests a case of suspected **pyogenic liver abscess** or **hepatic involvement** in a child, indicated by fever, rigors, and right upper quadrant tenderness without jaundice. The best initial investigation would help in confirming the diagnosis and guiding further management.

## **Why the Correct Answer is Right**
Ultrasonography (USG) of the abdomen is often the **first-line imaging technique** for evaluating suspected liver pathology, including abscesses, due to its non-invasive nature, wide availability, and ability to guide interventions. It can help identify liver abscesses, which are collections of pus in the liver, often presenting with fever, right upper quadrant pain, and sometimes jaundice. Given the child's symptoms and physical examination findings, an ultrasound can quickly assess for liver abscess or other pathology.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While a **Complete Blood Count (CBC)** can provide supportive evidence of infection (e.g., elevated white blood cell count), it does not directly diagnose the cause of the patient's symptoms.
- **Option B:** **Liver Function Tests (LFTs)** can indicate liver involvement but are not specific for diagnosing liver abscesses. They may show abnormal liver enzymes but do not provide a direct visualization of the liver pathology.
- **Option C:** **CT Abdomen** can be useful for detailed evaluation but is typically not the first line due to radiation exposure concerns, especially in children, and higher costs compared to USG.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **ultrasonography is the preferred initial imaging modality** for suspected liver abscess, especially in pediatric patients, due to its safety and efficacy. Early diagnosis and intervention are crucial to prevent complications.

## **Correct Answer:** D. Ultrasonography.