This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diabetes Mellitus, Subject name: Medicine
A 30 year old nurse is evaluated for recurrent hypoglycaemia. She feels shaky, anxious, and sweaty; her plasma glucose is 50 mg/dl during the attack at work. She then drinks coffee & feels better. These episodes have not happened outside the work environment. She takes no medications and is otherwise healthy. Which is the most appropriate test in this patient? 
Select and explain. 
A. Measurement of IGF-1, B. Measurement of fasting insulin and glucose levels, C. Measurement of fasting insulin, glucose, and C-peptide levels, D. Measurement of insulin, glucose, and C-peptide levels during a symptomatic episode
D: Measurement of insulin, glucose, and C-peptide levels during a symptomatic episode
Answer: D: Measurement of insulin, glucose, and C-peptide levels during a symptomatic episode 
Explanation: Whipple triad of symptoms: (1) Symptoms of hypoglycaemia (2) Low plasma glucose (3) Relief of symptoms with raising the plasma glucose level. The insulin levels must be obtained during an episode. If it is elevated, it suggests either endogenous hyperproduction of insulin or exogenous administration causing factitious hypoglycemia. C-peptide- determine normal cleavage of insulin from its precursor Normal C-peptide level with hypoglycaemia- surreptitious insulin use Low C-peptide level with hyperglycemia- pancreatic failure. Red flags in this case that point to surreptitious insulin use include the patient being a healthcare worker and the presence of symptoms only at work. Failure of counterregulatory hormones is rare cause of hypoglycaemia