I have been seen by the endocrinologist now. He has requested a 72 hour supervised fast. I was wondering what this test is used for? he is also measuring insulin, cpeptide and glucose levels along with ketones, what are all these used to indicate? please reply. thanks.

It's basically used to see how long you can go without eating until you drop, and how low you will drop.

Insulin levels indicate how much insulin is in your blood. They can see if it's too much. C-peptide measures how much of that insulin your body is naturally producing. In your case, it's to make sure you aren't injecting insulin to "fake" the hypoglycemia. Ketones are an indicator of whether or not your body is being forced to rely on sources other than carbs for energy. If you make it the whole 72 hours, you'll have some by then. If you get ketones when you go low, it could indicate ketotic hypoglycemia.