Glycemia

Glycemia or glycæmia is the concentration of glucose in the blood. It is usually expressed in milligrams per deciliter (mg/dl) in the US and other countries. It may also be expressed in millimol per decilitre (mmol/dl) especially in Europe. Both of these are SI units. It is one of the most important controlled variables in the internal milieu of animals (homeostasis), as it was first proposed by French physiologist Claude Bernard (1813-1878).

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Physiological regulation

Glycemia is controlled by several physiological processes. It tends to fluctuate to higher levels after meals, due to the gastric and intestinal absorption of carbohydrates of low molecular weight present in the diet or broken down from other kinds of foodstuffs, such as starches (polysaccharides), and to lower levels with usage by catabolism, particularly after stress, temperature regulation and physical exhertion. Another input to glycemia levels is gluconeogenesis, whereby glycogen stored in the liver and skeletal muscles, or aminoacids and lipids are converted to glucose via several metabolic chains. Excess glucose is converted to glycogen or to triglycerides for energy storage.

Glucose is the most important source of metabolic energy for the majority of cells, particularly for some cells (e.g., neurons and erythrocytes) which are almost totally dependent on it. The brain requires a fairly stable glycemia in order to function normally. Concentrations of less than about 30 mg/dl or greater than about 300 mg/dl can produce confusion, unconsciousness and convulsions.

Several hormones are involved in the regulation of glucose metabolism, such as insulin, glucagon (secreted by the pancreas), adrenalin (secreted by the adrenal glands), glucocorticoids and steroid hormones (secreted by the gonads and adrenal glands).

Measurement

For clinical evaluation purposes, there are two ways of measuring glycemia:

• Fasting glycemia: measured in a blood sample taken after 8 hours of complete fasting;
• Blood glucose tolerance test (OGTT): measured in several blood samples taken at intervals following a given glucose load (oral intake or endovenous injection).

In certain conditions, it is recommended that blood glucose monitoring be performed regularly, usually by the patient himself, who is trained to do a digital venipuncture and use a small portable glucometer device to evaluate glycemia levels instantly.

Glycemia fluctuates physiologically within a narrow range. Excessively low levels (e.g. a fasting glycemia of 70 mg/dl or below) are classed as hypoglycemia. These may result from poor diet, or as a side effect of diabetes medication. Excessively high levels (e.g., 250 mg/dl or more) are classed as hyperglycemia and are a particular threat to diabetes sufferers.

• 70-100 mg/dl: Normal
• 101-125 mg/dl: Impaired fasting glucose
• 126 mg/dl and above: Risk of diabetes

Abnormal values

Many forms of severe stress and trauma, stroke, heart attack, and surgery can temporarily increase glucose levels. Glycemia can also be increased by certain drugs such as antidepressants, corticosteroids, diuretics, estrogens, lithium, phenothiazine, phenytoin and Salicylic acids, or decreased by others, such as acetaminophen, alcohol, steroids, clofibrate, gemfibrozil.

However, the disease most directly associated to chronic increase of glycemia is diabetes mellitus, due to a decrease in the secretion of insulin, excess of its breakdown or decreased capacity of cells to transport it across its membranes (insulin resistance).

See also

• Hypoglycemia
• Hyperglycemia
• Glucose
• Diabetes
• Glycemic index
• Glycemic load