Oral Glucose Tolerance Test

Glucose Challenge Test, Glucose Tolerance Test, OGTT (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

Normal glucose levels in a blood sample taken from your vein (called a plasma glucose value) may vary from lab to lab.

Glucose challenge screening test (for gestational diabetes)

50 grams (g) of glucose	1-hour:	Less than 7.8 millimoles per litre (mmol/L) or 140 milligrams per decilitre (mg/dL)

If values are between 7.8–10.2 mmol/L (140–180 mg/dL), a glucose tolerance diagnostic test may be recommended.

 

Glucose tolerance diagnostic test (for gestational diabetes)

100 g of glucose	Fasting:	Less than 5.2 mmol/L or 95 mg/dL
	1-hour:	Less than 10.0 mmol/L or 180 mg/dL
	2-hour:	Less than 8.6 mmol/L or 155 mg/dL
	3-hour:	Less than 7.7 mmol/L or 140 mg/dL

 

Glucose tolerance screening test (for diabetes in women who have polycystic ovary syndrome)

75 g of glucose	2-hour:	Less than 7.8 mmol/L or 140 mg/dL

High values

High glucose levels may be caused by:

• Gestational diabetes.
• Polycystic ovary syndrome (PCOS).
• Taking medicines, such as corticosteroids, niacin, phenytoin (Dilantin), some diuretics, and some medicines used to treat high blood pressure, HIV, or AIDS.
• Severe stress.
• Large amounts of the hormone cortisol in the blood (Cushing's syndrome).
• Inherited diseases, such as cystic fibrosis, or hemochromatosis.
• Overproduction of growth hormone (acromegaly).
• Pheochromocytoma.

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.
• A condition that prevents the intestines from absorbing nutrients from food, such as celiac disease.
• Decreased production of the hormones cortisol and aldosterone (Addison's disease).
• Problems with the thyroid gland (hypothyroidism) or an underactive pituitary gland.
• A tumour of the pancreas (insulinoma).
• Inflammation and scarring of the liver (cirrhosis).

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

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Author:	Caroline Rea, RN, BS, MS	Last Updated: September 14, 2007
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine Alan C. Dalkin, MD - Endocrinology Andrew Swan, MD, CCFP, FCFP - Family Medicine
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