This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Medicine
[{'content': 'Which of the following is not used in diagonosis of insulinoma \nSelect and explain. \nA. 72 hows fasting blood glucose levels, B. C peptide levels, C. Insulin/glucose ratio, D. D-xylose test', 'role': 'user'}, {'content': 'Answer: D \nExplanation: These blood tests are needed to diagnose insulinoma: glucose insulin C-peptide If available, a proinsulin level might be useful, as well. Other blood tests may help rule out other conditions which can cause hypoglycemia Ref Davidson edition23rd pg837', 'role': 'assistant'}]