Glucose

The Glucose (blood/plasma) test, also known as blood glucose, blood sugar, fasting blood glucose, or fasting plasma glucose, is used to diagnose diabetes mellitus and to assess broader disorders of carbohydrate metabolism, including those associated with alcoholism. Clinicians use it to evaluate metabolic decompensation such as acidosis and ketoacidosis, dehydration, and coma; and to investigate hypoglycemia, including episodes related to insulinoma and neuroglycopenia. Screening and confirmation of hyperglycemia or hypoglycemia may be performed on fasting, random, or postprandial samples, with abnormal values confirmed on separate days or by an oral glucose tolerance test. The assay is also employed for ongoing monitoring of diabetes in conjunction with HbA1c and for gestational diabetes screening, typically performed at 24–28 weeks of pregnancy.

Glucose absorbed in the small intestine circulates as the chief energy substrate for most cells, and the central nervous system depends on a tightly regulated concentration to function normally. Insulin produced by the pancreas promotes cellular uptake of glucose and its storage as glycogen or triglycerides, whereas glucagon stimulates hepatic glycogenolysis and raises blood glucose during fasting. Homeostatic mechanisms typically keep concentrations within a narrow range; disruption leads to hyperglycemia or hypoglycemia. Marked departures from the normal range can result in organ dysfunction, neurologic injury, and coma. Persistent hyperglycemia contributes to microvascular and macrovascular complications affecting kidneys, eyes, heart, blood vessels, and peripheral nerves. In pregnancy, untreated hyperglycemia (gestational diabetes) increases the risk of fetal macrosomia and subsequent neonatal hypoglycemia.