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Oral Glucose Tolerance Test

How It Feels

You may find it hard to drink the extremely sweet glucose liquid. Some people feel sick after drinking the glucose liquid and may vomit. Vomiting may prevent you from completing the test on that day.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

You may feel faint from having several blood samples taken in one day. But the amount of blood taken will not cause significant blood loss or anemia.

Risks

Some people's blood glucose levels drop very low toward the end of the test. But some people feel like their sugar levels are low, when their levels actually are not low. Symptoms of low blood glucose include weakness, hunger, sweating, and feeling nervous or restless. If you develop these symptoms during the test, you may have your sugar level checked quickly with a glucose meter. If your level is very low, the test will be stopped.

There is very little risk of a problem from having blood drawn from a vein.

  • You may develop a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.
  • In rare cases, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.
  • Continued bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your health professional before your blood is drawn.

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)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

WebMD Medical Reference from Healthwise

Last Updated: July 05, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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