Blood Glucose Glucose is the principal source of energy for mammalian cells. The blood glucose concentration is influenced by hormones which facilitate its entry to or removal from the circulation. The hormones alter glucose uptake by cells (for energy production), and influence blood glucose by promoting or inhibiting glucose production and glycogen production and breakdown. The most important hormone causing a decrease in blood glucose is insulin. Insulin is produced by beta cells in the pancreatic islets. Insulin release is stimulated by glucose, amino acids and hormones (glucagon and gastrin). It is inhibited by hypoglycemia, stomatostatin and drugs. Corticosteroids and growth hormone inhibit insulin by causing peripheral insulin resistance. Insulin decreases blood glucose by promoting glucose uptake and use by liver, muscle and tissue cells. It also enhances triglyceride formation (by stimulating lipoprotein lipase). It promotes uptake of K+, phosphate and Mg+ by cells. It also inhibits glucose production by inhibiting gluconeogenesis and glycogenolysis. The main hormones opposing the action of insulin (and increasing blood glucose) are glucagon, epinephrine, growth hormone, corticosteroids, somatostatin (by inhibiting secretion of insulin) and thyroxine (by increasing sensitivity of cells to epinephrine).

Hormone	Glycogen	Glucose production	Glucose uptake	[Glucose]
Insulin	Synthesis	Decrease	Promotes	Decrease
Corticosteroids	No effect	Increase	Decrease	Increase
Catecholamines	Breakdown	Increase	Decrease	Transient increase
Growth hormone	Breakdown	Increase	Decrease	Increase
Glucagon	Breakdown	Increase	No effect	Increase

Sample considerations Serum - serum glucose values decrease rapidly in samples that have not been separated from the cellular constituents of blood. Glucose values decrease by 10% per hour if serum is left in contact with cells. Note that the decrease in glucose is enhanced in patients with increased leukocyte or platelet counts, even if collected into fluoride oxalate tubes. Sodium fluoride (NaF) at concentrations of 10 mg/dl blood will inhibit glucolysis by erythrocytes, leukocytes and platelets. However, sodium fluoride is hypertonic and causes lysis of red blood cells. This releases intra-erythrocyte water which dilutes the glucose concentration. Glucose concentrations in sodium fluoride samples are consequently lower than in promptly separated serum samples (by approximately 7-12%). Lipemia and hemolysis may interfere with methodology. This is instrument- and reagent-dependent. [Hypoglycemia] [Hyperglycemia]