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Oral Glucose Tolerance Test

Results

The oral glucose tolerance test (OGTT) measures the body's ability to use a type of sugar, called glucose, that is the body's main source of energy.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

But with screening for gestational diabetes, the American Diabetes Association has recommended specific glucose values be used for diagnosis. If any of your glucose values are higher than what is listed in the table, you will be diagnosed with gestational diabetes.

**Glucose tolerance diagnostic test (for gestational diabetes)** ^{Reference 1}
75 g of glucose	Fasting:	Less than 95 mg/dL or 5.3 mmol/L
	1-hour:	Less than 180 mg/dL or 10.0 mmol/L
	2-hour:	Less than 153 mg/dL or 8.5 mmol/L

You have prediabetes if the results of your oral glucose tolerance test are 140 to 199 mg/dL (2 hours after the beginning of the test).

High values

High glucose levels may be caused by:

Diabetes.
Gestational diabetes.
Hyperthyroidism.
Taking medicines, such as Reference corticosteroids Opens New Window, niacin, phenytoin (Dilantin), some Reference diuretics Opens New Window, and some medicines used to treat high blood pressure, HIV, or AIDS.
Large amounts of the hormone cortisol in the blood (Reference Cushing's syndrome Opens New Window).
Inherited diseases, such as Reference hemochromatosis Opens New Window.
Reference Pheochromocytoma Opens New Window.

Low values

Low glucose levels may be caused by:

Certain medicines, such as medicines used to treat diabetes, some blood pressure medicines (such as propranolol), and some medicines for depression (such as isocarboxazid).
Decreased production of the hormones cortisol and aldosterone (Reference Addison's disease Opens New Window).
Problems with the thyroid gland (Reference hypothyroidism Opens New Window) or an underactive Reference pituitary gland Opens New Window.
A tumor or other problems of the pancreas.
Liver disease.

Many conditions can change blood glucose levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.

By:	Reference Healthwise Staff	Last Revised: Reference July 5, 2011
Medical Review:	Reference E. Gregory Thompson, MD - Internal Medicine Reference Alan C. Dalkin, MD - Endocrinology