Glycemia refers to the concentration of sugar or glucose in the blood. In the United States and in many other countries, it is expressed as milligrams per deciliter (mg/dl). In many of the European countries blood glucose or sugar is also measured as millimol per decilitre (mmol/dl). These measurements are referred to as the SI units.

Blood glucose is one of the most important blood parameters to measure, as abnormal levels can cause severe complications.

Glycemic control in the body is achieved through several physiological mechanisms. Some examples of how the blood sugar level fluctuates and is controlled are given below:

• The blood sugar levels tend to drop to its lowest point in the morning, after a night of sleep and therefore hours of fasting.
• After a meal, glycemic levels increase as carbohydrates are broken down into simpler sugars such as glucose and absorbed from the intestine into the bloodstream.
• The glycemic level drops after a bout of severe exercise when the blood sugar is used as a source of energy for muscular activity.
• Extremely cold temperatures also cause much of the blood sugar to be used up, therefore lowering the blood glucose level.
• Glycemia levels are also affected by the process of gluconeogenesis, where glucose is produced from non-carbohydrate sources such as glycerol, fatty acids and glucogenic amino acids.
• In another metabolic pathway called glycogenolysis, glycogen in the liver is broken down to release glucose into the blood.

Glycemia is one of the most important parameters in homeostasis, since glucose is needed to provide the metabolic energy required for many cell functions. Several important hormones are involved in the regulation of blood glucose. One is insulin, which promotes the uptake of glucose from cells when the glucose level is raised. Another is glucagon, which has the opposite effect and increases the blood glucose level when it has dropped too low. Glucagon promotes the conversion of glycogen in the liver to glucose, which is then released into the bloodstream. Epinephrine also raises the blood sugar level, as do glucocorticoids and steroid hormones.