Glucose is a reducing monosaccharide sugar that serves as the principal source of energy for all the body tissues. There are two major peptide hormones secreted by the pancreas, insulin from the beta cells of islets of Langerhans and glucagon from the alpha cells of the islets of Langerhans whose coordinated functions regulate glucose metabolism. Glucose enters the cell through the influence of insulin and undergoes a series of reactions to produce energy thus insulin production occurs in conditions of high blood glucose levels and acts to reduce it. Lack of insulin or resistance to insulin at cellular level causes diabetes mellitus during which blood glucose levels increases in blood. Therefore, in diabetes mellitus the blood glucose levels are high. A decreased blood glucose level, hypoglycemia, is often associated with starvation, hyperinsulinanemia and those taking a high dose for insulin therapy. Plasma or blood glucose is measured mainly in the diagnosis and management of diabetes mellitus. GTT (Glucose tolerance test) measures the ability of the body to tolerate, or cope with, a standard dose of glucose.

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