Glucose

The plasma glucose test—also referred to as blood glucose or fasting plasma glucose—is used to diagnose and monitor disorders of carbohydrate metabolism, including diabetes mellitus, hyperglycemia, and hypoglycemia. It assists in assessing metabolic acidosis and diabetic ketoacidosis, dehydration, coma, and neuroglycopenic conditions, including hypoglycemia related to insulinoma, and is applied to monitor therapeutic interventions. Testing can be obtained as a fasting, random, or postprandial measurement, or performed as part of an oral glucose tolerance test. A diagnosis of diabetes requires confirmation with repeat testing on a separate day. Pregnant individuals are screened for gestational diabetes between 24–28 weeks of gestation.

Glucose is the primary fuel for human tissues. Dietary carbohydrates are broken down into glucose and other monosaccharides, absorbed in the small intestine, and delivered into the bloodstream. Pancreatic insulin promotes cellular uptake of glucose and directs surplus energy into storage as glycogen or, in adipose tissue, as triglycerides, thereby maintaining plasma glucose within a narrow physiologic range. When circulating glucose declines—for example, with prolonged fasting or strenuous exercise—pancreatic glucagon stimulates hepatic glycogenolysis to restore blood glucose. Disruption of the insulin–glucagon axis produces hyperglycemia or hypoglycemia. Marked departures from normal can result in organ dysfunction, neurologic injury, and coma. Persistently elevated glucose contributes to microvascular and macrovascular complications involving the kidneys, eyes, nerves, heart, and blood vessels. During pregnancy, hyperglycemia may develop as gestational diabetes. Without treatment, it is associated with fetal overgrowth and neonatal hypoglycemia, and maternal hyperglycemia may resolve after delivery.