This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Zollinger Ellision Syndrome, Subject name: Medicine
[{'content': 'Increased gastrin is seen in : \nSelect and explain. \nA. Zollinger -Ellison syndrome, B. Iron deficiency anaemia, C. Duodenal ulcer, D. Gastric cancer', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Most sensitive & specific method for identifying Zollinger Ellison syndrome is demonstration of an increased fasting serum gastrin concentration (> 150 pg/mL)', 'role': 'assistant'}]