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What is the Oral Glucose Tolerance Test

Currently there is only one test to check for any type of hypoglycemia (too low blood sugar). Known as the oral glucose tolerance test (or OGTT), it is a basic “stress test” for the pancreas to see how it reacts to an overload of sugar. It is also given as a diabetes (too high blood sugar) test, although generally a finger prick blood sugar monitor test will be able to clinically establish diabetes. The tests measure the amount of blood sugar in the plasma of the blood, standard practice to see how well (or how badly) the pancreas is working.


Hypoglycemia can be either fasting hypoglycemia or reactive hypoglycemia. Fasting hypoglycemia is where the patient has lower than normal blood sugar readings whether they have eaten or not. Reactive hypoglycemia is in reaction to eating, where the body pumps out more insulin than normal and drops the blood sugar reading to a lower number.

Hypoglycemia can be diagnosed in different ways, although many with hypoglycemia never get diagnosed. They can have readings of under 70 mg/dl or shows signs of hypoglycemia even though they aren’t testing at under 70 mg/dl.

Insulin Resistance

Insulin Resistance (IR) is where the body produces insulin, unlike in diabetes, but that insulin amount is not enough to have a normal reaction in the body. Therefore the pancreas is still producing insulin, but it is not into the levels needed to bring the blood sugar level down to where it needs to be.

Glucose Tolerance Test

The oral glucose tolerance test (OGTT) has the patient fasting for up to fourteen hours beforehand, allowing for only water. As soon as he arrives for the test he is given a blood sugar test to see his baseline number. Then a sugar solution is given orally. Blood is then retested many times. For diabetes, the important numbers will come two hours into the test. For hypoglycemia it is typically not until four to six hours later that blood sugar will drop.

Results of the OGTT

After the 2 hour mark in an oral glucose tolerance test, the test administrator can see a thumbnail view of what the test is going to end up telling him. These are some of the ranges that can happen.

Normal range – Under 110 mg/dl fasting, Under 140 at 2hrs

Impaired Fasting Glycemia range – Over 110 to under 126 mg/dl fasting, Under 140 at 2hrs

Impaired Glucose Tolerance range – Under 126 mg/dl fasting, Under or equal to 140 at 2hrs.

Diabetes range – Over or equal to 126 mg/dl fasting, Over or equal to 200 at 2hrs.