Glucose is the scientific name for the sugar that provides much of the energy needed by the human body. Too little blood glucose might indicate a health problem, and too much glucose could suggest diabetes, a disease in which the body can't effectively regulate glucose. One way doctors can diagnose diabetes is through a fasting glucose test. This test also can be used to monitor the effectiveness of diabetes treatments.
How a Fasting Glucose Test Works
A fasting glucose test involves taking a blood sample when the patient hasn't eaten for at least 8 hours. The blood sample is analyzed and the amount of glucose in the blood is reported in mg/dL. The test is usually performed in the morning when the patient hasn't had any food or drink, other than water, overnight. Such fasting causes the body to release a hormone called glucagon that in turn makes the body produce glucose. When glucose levels rise, a healthy person's body releases insulin to bring the glucose levels back down and keep everything stable. A person with diabetes either doesn't make enough insulin or the body doesn't process insulin properly. Glucose levels will remain high when a person with diabetes is fasting; the test will show those higher levels.
What Results Mean
According to the National Institutes of Health, a result between 70 to 100 mg/dL is considered normal for a fasting glucose test. Glucose levels between 100 to 125 mg/dL may indicate prediabetes or a risk of type 2 diabetes. A result of 126 mg/dL or greater often will mean a diagnosis of type 2 diabetes and discussion of a treatment plan with a physician. Blood glucose levels might also be too low. For a diabetic person, blood glucose below 70 mg/DL could indicate too much insulin is being taken or that medications need to be adjusted to prevent blood sugar from crashing. Low blood sugar could indicate an underactive thyroid or pituitary gland.