**Core Concept**
Acute cholecystitis is an inflammatory condition of the gallbladder, often caused by gallstones, which obstruct the cystic duct and lead to ischemia, necrosis, and subsequent inflammation of the gallbladder wall. Clinical manifestations of acute cholecystitis include severe right upper quadrant pain, fever, and leukocytosis.

**Why the Correct Answer is Right**
Jaundice is not typically the earliest symptom of acute cholecystitis. In fact, jaundice usually develops in advanced cases of biliary obstruction, such as in choledocholithiasis or cholangitis. This is because the gallbladder is not yet significantly impacted in acute cholecystitis, and the liver is still able to conjugate bilirubin and secrete it into the bile, preventing jaundice. The earliest symptoms of acute cholecystitis are usually related to the obstruction of the cystic duct and the subsequent inflammation of the gallbladder wall.

**Why Each Wrong Option is Incorrect**
**Option B:** Mild raise in serum bilirubin level is possible in early stages of acute cholecystitis, as the obstruction of the cystic duct can cause a mild increase in bilirubin levels. However, this is not a distinguishing feature of acute cholecystitis and can be seen in other conditions as well.
**Option C:** Right upper quadrant pain is a classic symptom of acute cholecystitis, resulting from the inflammation of the gallbladder and the surrounding tissues.
**Option D:** Vomiting is a relatively common symptom of acute cholecystitis, often occurring due to the severe pain and inflammation of the gallbladder.

**Clinical Pearl / High-Yield Fact**
A classic clinical pearl to remember is that jaundice is more commonly associated with advanced biliary obstruction, such as in choledocholithiasis or cholangitis, rather than acute cholecystitis.

**✓ Correct Answer: A. Jaundice is the earliest symptom**