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Diabetic Testing

To have a glucose tolerance test means having glucose administered to see how quickly it is cleared from the blood. The test is used to test for insulin resistance, diabetes and sometimes for reactive hypoglycemia. The glucose is given orally and is usually part of a group of tests.

To get ready for the diabetic test, you are asked to not restrict your carbohydrate intake for a few days or even weeks before you have the test. If you are not well you should not have the test since the results may not give a true reading of how your glucose metabolism is when you are healthy. A complete adult dose of the glucose should not be given to someone weighing less then 94 pounds because to much glucose may give a false positive result.

To have an OGTT test done you will have to have been fasting for at least eight to fourteen hours before the test. You are only able to drink water. Usually the test is done in the morning around seven or eight since glucose tolerance shows a different result in the afternoon. What’s known as a zero time blood sample is taken.

A glucose solution is given to drink. Usually it’s the standard dose of 1.75 grams per kilo of body weight. The maximum dose is 75 grams. The solution should be drunk within the first 5 minutes.

Blood is then taken at certain intervals so that blood sugar and sometimes insulin levels are determined. The number of samples and the intervals will vary depending on the tests that are done. When doing a diabetes screening, the main and most important sample is the second hour sample and the zero and two hour samples might be all that are collected. During a research setting, the samples could be drawn at many different times.

If sugar is found in the urine even though blood levels are normal, a condition known as renal glycosuria, more urine samples are taken for testing in addition to fasting and the two hour blood tests.

If the fasting levels read below 6.1, then these are good levels. If the levels are between 6.1 and 7.0 then they are considered to be on the border and are impaired. When the fasting levels are continually over the 7.0 level, then a person is usually diagnosed with diabetes.

The two hour level should normally be below 7.8. If the results of the tests indicate that the levels are between 7.8 and 11.1, then this is an indication of impaired glucose tolerance. Any levels which are above 11.1 at 2 hours will give a confirmation of a diagnosis of diabetes.

A standard 2 hour OGTT is usually enough to either confirm or exclude most forms of diabetes mellitus at all levels except the earliest level of development. Longer tests are sometimes used for any number of other reasons, such as determining reactive hypoglycemia. The levels of insulin are sometimes measured to indicate either resistance or deficiency of insulin.

Glucose tolerance test is sometimes used to support the diagnosis that both the doctor and the patient have already agreed on based on other forms of evidence. However, it is not adequate by itself to either confirm or rule out the diagnosis of reactive hypoglycemia as it is for diabetes.

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