A fasting blood glucose test is a procedure that measures the amount of glucose, or sugar, in your bloodstream. Along with a separate testing procedure called an oral glucose tolerance test, it is a standard step in diagnosing blood glucose elevations and diabetes. You may receive elevated readings on a fasting glucose test as the result of several disease processes or from using certain medications.
Fasting Glucose Testing
You may receive a fasting blood glucose test as part of a routine screening for diabetes or pre-diabetes, according the American Association for Clinical Chemistry's Lab Tests Online. Since diabetes presents no obvious symptoms in its early stages, blood testing is typically required to reveal its presence. You may also receive a fasting glucose test if you present symptoms of hyperglycemia, or high blood sugar, such as fatigue, blurred vision, increased thirst or urination and infections that heal more slowly than normal. In addition, you may receive a test if you experience fainting or unconsciousness, or if you show symptoms of hypoglycemia, or low blood sugar. Examples of these symptoms include hunger, anxiety, trembling, blurred vision, sweating and confusion.
Diabetes and Pre-Diabetes
A llab performs a fasting glucose test by using blood drawn after you have not eaten for at least eight hours, according to the National Diabetes Information Clearinghouse. Preferably, you will have the procedure done in the morning for maximum accuracy. Normal results from testing fall in a range between 70 and 99 deciliters of glucose per liter of blood, Lab Tests Online says. If you have a result that falls between 100 and 125 mg/deciliter, you may have a condition called impaired fasting glucose, or pre-diabetes. If your results equal 126 mg/deciliter or higher, you may have active type 2 diabetes.
Additional Causes
Lab Tests Online lists a number of medical conditions that can potentially cause elevated results on a fasting glucose test, including chronic kidney failure, acute stress, overactive thyroid function, acute or chronic pancreas inflammation, pancreatic cancer, Cushing syndrome and a growth disorder called acromegaly. You can also receive an elevated result if you take medications such as lithium, corticosteroids, birth control pills, tricyclic antidepressants, diuretics, salicylates and epinephrine. Excessive food intake may also trigger heightened fasting glucose results.
Insulin Resistance
If you have pre-diabetes, your body may be abnormally resistant to the effects of insulin, the hormone your body uses to control glucose in your bloodstream, the National Diabetes Information Clearinghouse says. You may develop insulin resistance for reasons that include genetic inheritance, insufficient physical activity and carrying excessive amounts of body weight. If you are overweight, you probably will develop type 2 diabetes unless you lose 5 to 7 percent of your total body weight within 10 years of a pre-diabetes diagnosis, according to the clearinghouse.
Oral Glucose Tolerance
If your doctor administers an oral glucose tolerance test, you will undergo a period of fasting, and then drink a sweet liquid, according to the National Diabetes Information Clearinghouse. Two hours later, the doctor will test your blood glucose. Pre-diabetic results from this procedure range from 140 to 200 mg/deciliter. Results above 200 mg/deciliter indicate the possible presence of diabetes.
