**Obstructive Jaundice Initial Investigation**

**Core Concept**
Obstructive jaundice occurs when there is a blockage in the bile ducts, leading to a buildup of bilirubin in the blood and subsequent jaundice. The initial investigation aims to confirm the diagnosis and identify the level and cause of obstruction.

**Why the Correct Answer is Right**
The most appropriate initial investigation for obstructive jaundice is an ultrasound of the abdomen. This is because ultrasound is non-invasive, widely available, and can provide valuable information about the anatomy of the bile ducts, liver, and gallbladder. It can also help identify signs of obstruction, such as dilated bile ducts or gallstones. In addition, ultrasound can guide further diagnostic procedures, such as fine-needle aspiration or percutaneous transhepatic cholangiography.

**Why Each Wrong Option is Incorrect**
* **Option A:** CT scan of the abdomen. While CT scans can provide detailed images of the abdominal organs, they are not the first-line investigation for obstructive jaundice due to their higher cost and radiation exposure.
* **Option B:** ERCP (Endoscopic Retrograde Cholangiopancreatography). ERCP is a more invasive procedure that is usually reserved for therapeutic purposes, such as removing bile duct stones or stenting a stricture. It is not the initial investigation for obstructive jaundice.
* **Option C:** Liver function tests (LFTs). While LFTs can provide information about liver function and may be abnormal in obstructive jaundice, they do not directly diagnose the cause of obstruction.

**Clinical Pearl / High-Yield Fact**
Remember that ultrasound is the first-line investigation for obstructive jaundice because it is non-invasive, widely available, and can provide valuable information about the anatomy of the bile ducts.

**Correct Answer:** A. Ultrasound of the abdomen.