In some patients, the level of dissolved glucose in the blood, or the blood sugar level, must be monitored to insure that the patient does not suffer side effects due to a lack of glucose in the blood (hypoglycemia) or an excess of glucose in the blood (hyperglycemia). Either can cause a loss of consciousness and lead to coma.

In a normal human body, two hormones, insulin and glucagon, regulate the amount of sugar in the blood no matter when a patient has last consumed carbohydrates. It is generally maintained between 70-150 milligrams of glucose for every decilitre (1/10th of a litre) of blood. Insulin allows cells to take in more sugar, lowering the level in the blood, while glucagon reduces the ability of cells to taken in glucose.

However, a number of conditions, the chief of which is diabetes mellitus, result in one or the other hormone not being produced by the body, generally meaning it has to be injected into the patient in order to restore blood sugar to the proper level. In a person with a blood sugar condition in the long term, diet is the most important factor in regulating blood sugar. Persons who tend to hypoglycemia must eat regularly and avoid skipping meals. Persons who tend to hyperglycemia must both eat regularly, inject insulin on a consistent basis, and avoid foods that are high in carbohydrates.

Blood sugar can be measured in a number of ways, such as by directly testing the blood or urine. However, if a person is suspected to have a blood sugar regulation problem, they are usually given a glucose tolerance test, which consists of testing the blood before a dose of glucose and at regular intervals thereafter.

Diabetics can suffer from both conditions, as injecting insulin without eating will cause the blood sugar level to drop to dangerous levels.

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