Sugar is the primary fuel your body uses to generate the energy-releasing chemicals needed to keep your organs and tissues functioning. Your body normally maintains your blood sugar level within a narrow range through the secretion of hormones. An abnormally elevated or depressed blood sugar level --- hyperglycemia and hypoglycemia, respectively --- may indicate a serious medical condition. The healthy range for blood sugar varies, depending primarily on whether you are fasting.
Fasting Blood Sugar
A fasting blood sugar test, also known as an FBS or FBG, measures the concentration of glucose in your blood after you have not eaten for at least eight hours. The test is typically performed in the early morning, before you have breakfast. A normal FBS is 70 to 99 milligrams per deciliter, written as mg/dL. An FBS of 126 mg/dL or greater on two separate occasions usually indicates that you have diabetes mellitus. A fasting blood sugar level of 100 to 125 mg/dL indicates a condition called prediabetes, wherein your blood sugar level is elevated but not to the point of constituting diabetes. If you have prediabetes, you are at increased risk of developing type 2 diabetes. Reducing your intake of added sugars and fats, losing weight and engaging in regular physical activity can prevent or delay progression to type 2 diabetes.
Random Blood Sugar
Blood sugar levels are usually most helpful for diagnostic purposes when evaluated in relationship to when you last ate. Occasionally, however, your doctor may order a glucose test regardless of the timing of your last meal. This test, known as a random or casual blood sugar, is normally less than 140 mg/dL. A random blood sugar level of 200 mg/dL or greater with symptoms of hyperglycemia --- including thirst, hunger, fatigue, frequent urination and weight loss --- usually indicates that you have diabetes.
Oral Glucose Tolerance Blood Sugar Levels
If your doctor suspects that you have a problem with blood sugar regulation, she may order an oral glucose tolerance test, often abbreviated OGTT. After an 8-hour fast, you are given a sweet solution to drink, which typically contains 75 g of glucose. A laboratory technician draws a blood sample every 30 to 60 minutes for up to three hours after drinking the glucose solution. One hour after consuming the test solution, a normal blood sugar level is less than 200 mg/dL. At the 2-hour mark, a normal glucose level is less than 140 mg/dL. A 2-hour result greater than 200 mg/dL typically indicates diabetes. If your 2-hour OGTT level is 140 to 200 mg/dL, you may have prediabetes.
Hypoglycemia
Hypoglycemia most commonly occurs in diabetics and is caused by a reaction to blood sugar medication. For diabetics, a blood sugar level of less than 70 mg/dL constitutes hypoglycemia. If you are not diabetic, a fasting blood sugar level of less than 50 mg/dL usually indicates significant hypoglycemia. A form of hypoglycemia known as reactive hypoglycemia is diagnosed when three criteria are met: The blood sugar level is less than 70 mg/dL at a time when you are experiencing hypoglycemic symptoms, such as hunger, shakiness, sweating, irritability and confusion; the symptoms resolve after eating; and the resolution of symptoms is accompanied by a rise in your blood sugar level to greater than 70 mg/dL. Although people sometimes presume they have hypoglycemia, the condition is rare if you do not have diabetes. Many people with fasting and between-meal blood sugar levels of 60 to 70 mg/dL have no symptoms of hypoglycemia and are completely healthy.
References
- "Diabetes Care"; Diagnosis and Classification of Diabetes Mellitus; American Diabetes Association; December 30, 2010
- MedlinePlus; Glucose Test - Blood; David C. Dugdale III, M.D.; May 23, 2010
- MedlinePlus; Glucose Tolerance Test; David C. Dugdale III, M.D.; May 23, 2010
- National Institute of Diabetes and Digestive and Kidney Diseases: Hypoglycemia
- Virginia Mason Medical Center: What Are Normal Blood Glucose Levels?
- Lab Tests Online: Glucose Tests
