The job of insulin is to take care of the extra sugar or glucose that you consume. Your body needs glucose for energy. But it cannot consume all the glucose that it gets. Insulin breaks down the access glucose and stores them so that later, when you need energy, you can get it. When insulin is unable to do so or when there is scarcity of insulin in your body, your blood sugar levels increase. A Glucose F test can tell you if there is some problem with your insulin.