Around 23.8 million Americans had diabetes in 2007, according to the American Diabetic Association. Because type 2 diabetes, formerly known as adult onset diabetes, may not cause any symptoms in its early stages, blood tests such as the glucose tolerance test are often used to assess whether a person has type 2 diabetes or is at risk of developing the disease.
Purpose
The oral glucose tolerance test analyzes blood levels before and after eating to assess the rise in blood sugar after drinking a glucose laden drink. The tests also measures how quickly blood glucose levels return to baseline and compares the result to an average found in people without diabetes.
Procedure
The person taking the glucose tolerance test fasts for at least eight to 10 hours and then has blood drawn. He then consumes a drink or snack containing 75-grams of glucose. Blood glucose levels are drawn up to four times after consuming the glucose solution.
Time Frame
It's important to follow timing instructions exactly or the result of the glucose tolerance test won't be accurate. Fasting for less than eight to 10 hours can cause the fasting blood sugar to be elevated, indicating diabetes even if the person doesn't have it, because blood glucose rises after eating and then falls over several hours. Even a few sips of coffee with sugar or a soda can raise blood glucose levels. The subsequent blood tests must be drawn at the proper times, because blood glucose results are compared to a "norm" based on a certain amount of time.
Results
Fasting blood glucose levels should fall between 60 and 100 mg/dl. Levels of 126 mg/dl or higher indicate diabetes, while numbers between 100 and 126 indicate pre-diabetes, also known as impaired glucose tolerance, the strong potential to develop diabetes. After one hour, levels should be less than 200 mg/dl. Levels at two hours should be less than 140 mg/dl; levels between 140 and 200 mg/dl indicate pre-diabetes and levels over 200 mg/dl indicate diabetes. Levels must be confirmed with a second test.
Implications
Most people diagnosed with pre-diabetes or impaired glucose tolerance develop diabetes within 10 years unless they make lifestyle changes such as losing 5 percent to 10 percent of body weight and increasing physical activity. Losing 5 percent to 7 percent of body weight can reduce or postpone the risk of developing diabetes by 60 percent, the National Institute of Diabetes and Digestive and Kidney Disorders states.
Considerations
Some people get sweaty and nauseated after drinking the glucola. Tests results can be altered by taking certain medications, such as corticosteroids, thiazide diuretics, oral contraceptives or beta blockers, MedlinePlus states.
