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
Increased gastrin is seen in : 
Select and explain. 
A. Zollinger -Ellison syndrome, B. Iron deficiency anaemia, C. Duodenal ulcer, D. Gastric cancer
A: Zollinger -Ellison syndrome
Answer: A: Zollinger -Ellison syndrome 
Explanation: Most sensitive & specific method for identifying Zollinger Ellison syndrome is demonstration of an increased fasting serum gastrin concentration (> 150 pg/mL)