Glucose, the primary energy source for human and animal cells, is a type of sugar that travels through the bloodstream. Glucose enters your body whenever you eat carbohydrate foods. Glucose levels are regulated by insulin and glucagon. Insulin is a hormone that is produced by the pancreas and released into the bloodstream when glucose levels rise.

Normal glucose levels fall between 70 and 150 mg. Levels typically are lower in the morning, and rise after meals. Blood sugar levels falling consistently above 150 are indicative of hyperglycemia, or high blood sugar. Chronic low levels, falling below 70, characterize hypoglycemia, or low blood sugar. Hypoglycemia is a potentially fatal condition. Symptoms of this condition are lethargy, impaired mental functioning, irritability and loss of consciousness. Persistent hyperglycemia results in diabetes mellitus, which is the most common disease related to blood sugar regulation failure. Diabetes can cause eye, kidney and nerve damage.

A blood glucose test measures the amount of glucose in the bloodstream. Reasons for testing glucose levels are to check for diabetes, to monitor treatment of diabetes, and to check for hypoglycemia. There are several different types of glucose tests. The 'fasting blood sugar' test checks glucose levels after an eight-hour fast and is often the first test performed when checking for diabetes. For this test, levels have to fall between 70 and 99 in order to be considered normal. The 'two-hour postprandial blood sugar' test measures glucose levels two hours after eating a meal.

Normal glucose levels for this test fall between 70 and 145. Random blood sugar testing checks glucose levels randomly throughout the day, regardless of meal times. If levels vary widely, there could be a problem. Blood sugar levels should be between 70 and 125 in order to be considered normal for random testing. The 'oral glucose tolerance test' diagnoses diabetes and predicaments. This tests your blood after drinking a glucose drink. If you think you may have a blood sugar disorder, contact your primary care physician for testing. There are many conditions that can cause a change in your blood glucose levels. Normal results may vary depending on the lab.