This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastro Intestinal System, Subject name: Pediatrics
A 17-year-old adolescent female is 6 weeks postpartum. She presents to the emergency room with the complaints of increased jaundice, abdominal pain, nausea, vomiting, and fever. Her examination is remarkable for jaundice, pain of the right upper quadrant with guarding, and a clear chest. Chest radiographs appear normal. Which of the following tests is most likely to reveal the cause of this pain? 
Select and explain. 
A. Serum chemistries, B. Complete blood count (CBC) with platelets and differential, C. Ultrasound of the right upper quadrant, D. Upper GI series
C: Ultrasound of the right upper quadrant
Answer: C: Ultrasound of the right upper quadrant 
Explanation: Cholecystitis and cholelithiasis are unusual diseases in children and are almost always associated with predisposing disorders such as hemolytic anemia, pregnancy, CF, Crohn disease, obesity, rapid weight loss, or prior ileal resection. Pain of the right upper quadrant, nausea, vomiting, fever, and jaundice are symptoms of acute cholecystitis. The diagnosis is confirmed with an ultrasound of the gallbladder. While some of the other answers listed might result in abnormalities, the findings would be neither sensitive nor specific for cholecystitis. Thus, the diagnostic test of choice is an ultrasound.