normally, or there is not being enough produced. pancreatic cancer pancreatitis underactive thyroid Low blood sugar may indicate insulin overuse starvation underactive thyroid Addison's disease insulinoma kidney disease Preparing for testing Fasting prior to glucose testing may be required with some test types. Fasting blood sugar test, for example, requires 10–16 hour-long period of not eating before the test. Blood sugar levels can be affected by some drugs and prior to some glucose tests these medications should be temporarily given up or their dosages should be decreased. Such drugs may include salicylates (Aspirin), birth control pills, corticosteroids, tricyclic antidepressants, lithium, diuretics and phenytoin. Some foods contain caffeine (coffee, tea, colas, energy drinks etc.). Blood sugar levels of healthy people are generally not significantly changed by caffeine, but in diabetics caffeine intake may elevate these levels via its ability to stimulate the adrenergic nervous system. Reference ranges Fasting blood sugar A level below 5.6 mmol/L (100 mg/dL) 10–16 hours without eating is normal. 5.6–6 mmol/L (100–109 mg/dL) may indicate prediabetes and oral glucose tolerance test (OGTT) should be done for high-risk individuals (old people, those with high blood pressure etc.). 6.1–6.9 mmol/L (110–125 mg/dL) means OGTT should be done even if other indicators of diabetes are not present. 7 mmol/L (126 mg/dL) and above indicates diabetes and the fasting test should be repeated. Glucose tolerance test Postprandial glucose test Random glucose test See also Hyperglycemia Hypoglycemia References Blood tests