A blood glucose fasting test is normally done if a person shows signs of diabetes, prediabetes, experiences fainting spells or has a seizure, notes Healthline. Other reasons for the test may include checking a person for hypoglycemia, monitoring current diabetes treatment or checking for gestational diabetes, according to WebMD.
Insulin is released into a person's bloodstream when the amount of glucose in the blood rises, states WebMD and Healthline. Glucose is created from carbohydrates and is the main energy source for the human body. A person who has diabetes has abnormally high glucose levels. Normally, insulin controls the level of glucose in the body. Diabetic people either do not produce enough insulin or the insulin does not work as it should. Untreated diabetes and high glucose levels can lead to organ damage.