Assessment of blood sugar levels, or glucose test is done to measure the amount of glucose dissolved in the blood and is expressed in milli moles per liter (mmol / l). Blood glucose level are also expressed in grams per liter (i.a. in France) or in milligrams per deciliter (i.e., Germany, Belgium). The result, normal or abnormal, is determined, depending on the unit of measure used. A normal fasting value lies between 4.0 and 7.0 mmol / l. To get an accurate value, the blood glucose level is measured on an empty stomach.

A person has diabetes (diabetes mellitus) if the "fasted" values in an untreated case are above 7.0 mmol / l, and "non-fasted", above 12.0 mmol / l.

Blood glucose levels vary during the day. When waking up in the morning the levels are low, and after the first meal, it begins to rise. This is because glucose is absorbed into your bloodstream, from the food that you eat. All cells in the human body, use glucose for energy. The brains, the main body parts, depends on glucose for its energy needs.

The hormone insulin, which is produced by the islets of Langerhans, in the pancreas, stimulates the uptake of glucose from the blood into the cells, thus providing them with the necessary energy.

Furthermore, insulin makes sure that the excess glucose in the blood, liver and muscle cells are stored as glycogen, so that the blood sugar levels fluctuate as little as possible.

Under the influence of the hormone glucagon and adrenaline, glycogen is stored in the cells so that it can be turned into glucose again when there is a shortage in the blood (glycogenolysis) Glucagon is also produced by the islets of Langerhans. 

The body can also make, glucose via gluconeogenesis.

In people with diabetes mellitus (“diabetes"), the pancreas creates insufficient amounts of insulin, or the cells (the insulin receptors) are insensitive to the insulin.

People with diabetes may experience hypoglycemia (low blood sugar), which can be remedied by eating or drinking products that are sweet. They may also experience, hyperglycemia (high blood sugar) in which case carbohydrates should be avoided

Hypoglycemia is dangerous because the brains need sufficient glucose to function.

Long term Hyperglycemia causes all sorts of problems, especially in the blood vessels of the eyes, kidneys, legs and cardiovascular system. Poorly managed diabetes leads to deterioration of the nerves. It is wise to regularly test your blood sugar levels, on an empty stomach, to know if you have diabetes.