Your cells contain microscopic powerhouses that convert the sugar glucose into the energy needed to fuel your metabolic and physical activities. To ensure no interruption in energy production, your blood glucose level is normally maintained within a narrow range by the pancreatic hormones insulin and glucagon. Blood glucose levels consistently outside the normal range for nondiabetics may indicate the development of a potentially serious medical problem.
Fasting Blood Glucose
A fasting blood glucose is the concentration of the sugar in your blood after you have not had anything to eat or drink --- other than water --- for at least eight hours. The upper normal limit for fasting blood glucose, or FBG, in nondiabetics is 99 mg/dL. If your FBG is 100 to 125 mg/dL, you have impaired glucose tolerance or prediabetes, which means your body is not metabolizing glucose normally. Lifestyle changes, including regular physical activity, eating a healthful diet and modest weight loss, may correct your blood glucose level and prevent the development of Type 2 diabetes if you have impaired glucose tolerance.
Low Blood Glucose
Hypoglycemia, or an abnormally low blood sugar level, is uncommon in nondiabetics. Reactive hypoglycemia is diagnosed if your blood sugar level drops below 70 mg/dL and you experience related symptoms, such as shakiness, sweating, nervousness, dizziness and confusion. With reactive hypoglycemia, symptoms characteristically develop within four hours after meals and are relieved by eating.
Another type of hypoglycemia that occurs in nondiabetics is fasting hypoglycemia, defined as a blood glucose level of less than 50 mg/dL after not eating for eight hours or longer. Binge drinking, starvation, serious infections, insulin-secreting tumors and certain medications can cause fasting hypoglycemia.
Glucose Tolerance Test
Your doctor may order a glucose tolerance test to check your blood glucose level if she is concerned about your sugar metabolism. After an overnight fast, you go the testing site and drink a solution that typically contains 75 g of glucose. Your blood sugar level is checked at regular intervals after you drink the solution to determine how your body handles the glucose load. Your glucose level two hours into the test is particularly important for determining if you have diabetes.
A normal blood glucose level two hours after a 75-g "challenge" is less than 140 mg/dL, if you are not pregnant. A level of 140 to 199 mg/dL at two hours indicates that you have impaired glucose tolerance.
Pregnancy
Pregnancy alters your body's handling of glucose to ensure that the baby has an adequate supply of sugar. Therefore, the normal blood glucose levels for pregnant, nondiabetic women are slightly different than for other adults. A normal FBG for a nondiabetic woman during pregnancy is less than 95 mg/dL. With a 75-g oral glucose tolerance test, a normal one-hour level is less than 180 mg/dL and a normal two-hour level is less than 155 mg/dL.
References
- "Endocrine Practice"; American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for the Management of Diabetes Mellitus; Helena W. Rodbard, M.D., et al.; May--June 2007
- "Diabetes Care"; Diagnosis and Classification of Diabetes Mellitus; American Diabetes Association; December 2010
- National Institute of Diabetes and Digestive and Kidney Diseases: Hypoglycemia
