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What Is the Oral Glucose Tolerance Test?

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Although doctors don't routinely use it anymore, the oral glucose tolerance test is the gold standard for diagnosing type 2 diabetes. It's still commonly used to diagnose gestational diabetes, a condition that a woman can get while pregnant.

You’ll fast for at least 8 hours -- but not more than 16 -- the night before you take the test. When you get to the doctor’s office, he’ll test your fastingblood sugar. Afterward, you’ll get 75 grams of glucose (100 grams for pregnant women), usually in the form of a sweet-tasting liquid that you drink. The doctor will take blood samples up to four times to measure your blood sugar levels.

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Obstetricians use several methods to do this test, but the one described here is standard.

How Reliable Is the Test?

For the oral glucose tolerance test to give reliable results, you have to be in good health. You can’t have any other illnesses -- not even a cold. And you can’t be taking drugs that could affect your blood sugar.

You'll have to watch your carbs beforehand, too. Don’t eat more than 150 to 200 grams a day for 3 days before the test. Don’t smoke or drink coffee the morning of the test, either.

What Does It Measure?

The classic oral glucose tolerance test measures blood sugar levels over a period of 3 hours. Some doctors simply get a beginning blood sample, followed by a sample 2 hours after you drink the glucose solution.

If you don’t have diabetes, your blood sugar levels will rise and then fall quickly. If you do have it, the levels rise higher than normal don’t come back down as fast.

If the test shows that your levels are between normal and diabetic, you have what doctors call impaired glucose tolerance (IGT). People with IGT don’t have diabetes yet.

If you have a high blood sugar level, weight loss and exercise may help return it to normal. Some doctors suggest medications like metformin (Glucophage) to help prevent or delay the onset of diabetes.

WebMD Medical Reference from MedicineNet

Reviewed by Michael Dansinger, MD on December 24, 2013
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If the level is below 70 or you are experiencing symptoms such as shaking, sweating or difficulty thinking, you will need to raise the number immediately. A quick solution is to eat a few pieces of hard candy or 1 tablespoon of sugar or honey. Recheck your numbers again in 15 minutes to see if the number has gone up. If not, repeat the steps above or call your doctor.

People who experience hypoglycemia several times in a week should call their health care provider. It's important to monitor your levels each day so you can make sure your numbers are within the range. If you are pregnant always consult with your health care provider.

Congratulations on taking steps to manage your health.

However, it's important to continue to track your numbers so that you can make lifestyle changes if needed. If you are pregnant always consult with your physician.

Your level is high if this reading was taken before eating. Aim for 70-130 before meals and less than 180 two hours after meals.

Even if your number is high, it's not too late for you to take control of your health and lower your blood sugar.

One of the first steps is to monitor your levels each day. If you are pregnant always consult with your physician.

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