Glucose testing is performed to monitor blood sugar levels in people with diabetes as well as to screen for diabetes. Glucose testing is done randomly or after fasting for eight hours. A physician will determine which method of testing is needed for a patient's situation.
According to MedlinePlus.com, a normal blood sugar level before meals is between 70 to 130 milligrams per decilitre (mg/dl) and after meals is less than 180 mg/dl.
According to the ninth edition of Mosby's Diagnostic and Laboratory Test Reference, critical blood glucose levels for an adult male are less than 50 mg/dl or greater than 400 mg/dl. Critical glucose levels for an adult female are and less than 40 mg/dl or greater than 400 mg/dl.
According Mosby's Diagnostic and Laboratory Test Reference, forms of stress such as general anaesthesia, stroke or heart attack can increase glucose levels in the blood.
Increased levels of glucose may signify diabetes mellitus, Cushing's syndrome, pheochromocytoma, chronic renal failure, glucagonoma, acute pancreatitis, diuretic therapy, corticosteroid therapy and acromegaly.
Decreased levels of glucose may indicate insulinoma, hypothyroidism, hypopituitarism, Addison's disease, extensive liver disease, insulin overdose and starvation.