Levels vary according to the laboratory, but in general up to 100 milligrams per deciliter (mg/dL) are considered normal.

Persons with levels between 100 and 126 mg/dL may have impaired fasting glucose or prediabetes. These levels are considered to be risk factors for type 2 diabetes and its complications.

Diabetes is typically diagnosed when fasting blood glucose levels are 126 mg/dL or higher.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Greater than normal levels (hyperglycemia) may indicate:

• Acromegaly (very rare)
• Cushing syndrome (rare)
• Diabetes mellitus
• Impaired fasting glucose (also called "prediabetes")
• Hyperthyroidism
• Pancreatic cancer
• Pancreatitis
• Pheochromocytoma (very rare)
• Too little insulin
• Too much food

Lower than normal levels (hypoglycemia) may indicate:

• Hypopituitarism
• Hypothyroidism
• Insulinoma (very rare)
• Too little food
• Too much insulin

This test also may be performed for:

• Acute adrenal crisis
• Cushing syndrome caused by adrenal tumor
• Cushing syndrome - exogenous
• Delirium
• Dementia
• Dementia due to metabolic causes
• Diabetic hyperglycemic hyperosmolar coma
• Diabetic ketoacidosis
• Diabetic nephropathy/sclerosis
• Ectopic Cushing syndrome
• Epilepsy
• Generalized tonic-clonic seizure
• Glucagonoma
• Islet of Langerhans' tumor
• Multiple endocrine neoplasia (MEN) I
• Pituitary Cushing's (Cushing's disease)
• Syphilis
• Syphilis - primary
• Syphilis - secondary
• Syphilis - tertiary
• Type 1 diabetes
• Type 2 diabetes
• Transient ischemic attack (TIA)