An Insulin Fasting Lab test is done to evaluate insulin production by the Beta cells in the pancreas. It is also practiced to help determine the cause of low blood glucose, which is a disease known as Hypoglycemia. It is also performed to help diagnose the presence of an insulin-producing tumor in the Pancreas called Insulinoma which in fact causes Hypoglycemia, and also to identify the insulin resistance or to help determine when a type II diabetic might need to start taking insulin to supplement oral medications. It is advisable to take the insulin fasting test when you have low blood glucose levels with symptoms such as sweating, palpitations, dizziness, fainting; when you have diabetes and your insulin production needs to be monitored; sometimes when it is suspected that you have insulin resistance.