A fasting blood glucose level of less than 100 mg/dL is considered to be normal, according to Medline Plus. A level between 100 mg/dL and 125 mg/dL indicates impaired fasting glucose, or prediabetes. There are many causes of high blood glucose levels, with diabetes being the most common. Other causes of increased glucose levels, or hyperglycemia, include glucagonoma, hyperthyroidism, acromegaly, Cushing syndrome and medications.
Diabetes
Medline Plus states diabetes is diagnosed when the fasting blood glucose level is above 126 mg/dL. The University of Maryland Medical Center explains people with diabetes either do not produce enough insulin, or they cannot use the insulin that their bodies produce. Consequently, glucose, or sugar, builds up in the bloodstream. There are two major types of diabetes, Type 1 and Type 2. Type 2 is far more common, and makes up more than 90 percent of the cases. Kidshealth.org lists several reasons why hyperglycemia occurs in diabetics. The first cause can occur when the diabetic does not take his medication at the right time, or take the right amounts. The second reason happens when the diabetic does not follow her meal plan, eats too much or the wrong kinds of foods. Other reasons a diabetic can develop hyperglycemia include not exercising enough, illness and stress.
Acromegaly
The Mayo Clinic describes acromegaly as a rare hormonal disorder that occurs when the pituitary gland produces too much growth hormone; this usually happens as a result of a benign tumor. Diabetes or high blood sugar can result from this disorder. All of the endocrine glands in the body work together, so when one is affected, it can cause disorders in the others. Occasionally, acromegaly is caused by nonpituitary tumors, such as in the pancreas, where insulin is made. This causes the body to not utilize insulin as it should, resulting in hyperglycemia.
Cushing Syndrome
Cushing syndrome is a disorder that occurs when the body is exposed to high levels of cortisol hormone, states Medline Plus. It can also occur with the intake of cortisol or steroid medications. High blood sugar occurs in laboratory tests with Cushing syndrome, and diabetes is a potential complication. Cushing syndrome can be caused by an adrenal gland tumor, or a pituitary gland tumor, which affects the endocrine system.
Glucagonoma
The New York Times describes a glucagonoma as a very rare tumor of the islet cells of the pancreas. These cells release the hormones insulin and glucagon. Of these tumors, 60 percent are cancerous and the cancer tends to spread to the liver. Signs of a glucagonoma include glucose intolerance and hyperglycemia, or elevated blood glucose levels.
Hyperthyroidism
According to "Clinical Diabetes," hyperthyroidism is typically associated with worsening glycemic control and increased insulin requirements. They state diabetic patients have a higher prevalence of thyroid disorders compared with the normal population. Hyperglycemia may improve in these hyperthyroid patients as they are treated for the thyroid disease. Also, if a diabetic patient develops worsening hyperglycemia, hyperthyroidism should be considered.
Other Causes
Other causes of hyperglycemia include severe stress such as trauma, stroke, heart attack or surgery and any pancreas disorders, including cancer or infection. Medline Plus lists several medications that can cause an increase in glucose levels, such as risperidone, diuretics, epinephrine, estrogens, lithium, dilantin, aspirin and tricyclic antidepressants.
