Glucose Tolerance Test (oGTT)

How is diabetes mellitus detected?

Professionals have agreed internationally on certain blood glucose levels, from which the diagnosis of diabetes is made. For example, as the blood glucose level rises sharply after a meal and then drops, the threshold also depends on how long the last meal has been.

Fasting blood sugar

This measurement takes place, for example, in the morning before breakfast. The diagnosis of diabetes is made when the fasting blood glucose level repeatedly exceeds 126 mg / dL (corresponds to 7 mmol / L).

Glucose tolerance test

How well the body can process sugar can also be determined by a so-called oral glucose tolerance test (oGTT). You drink a glass of water in which 75 grams of glucose are dissolved. After that, the blood sugar rises but should fall quickly again. The diagnosis of diabetes is made when the blood sugar after two hours is still over 200 mg/dl (equivalent to 11.1 mg / L).

Opportunity measurement

The blood glucose value is often also determined when blood was taken for other reasons. Diabetes is suspected if glucose is above 200 mg / dL (equivalent to 11.1 mg / L) on such occasional measurements. As a rule, physicians then propose the measurement of fasting blood glucose or a glucose stress test for review.


HbA1c is a part of the red blood pigment (hemoglobin) to which sugar molecules can adhere. The HbA1c value indicates how high the blood glucose has been on average in the last three months. The diagnosis of diabetes is made when the HbA1c value is above 6.5%.

Glucose Tolerance Test: What’s the exact procedure?

An oral glucose tolerance test (oGTT) is designed to measure how well the body can handle a more significant amount of sugar. It is therefore also called glucose load test. If the blood glucose in the test exceeds specific values, it may be that the sugar is not sufficiently absorbed into the body cells. You may have diabetes mellitus or gestational diabetes.

In gestational diabetes, blood sugar levels are elevated, usually due to altered metabolism during pregnancy. After the birth of the child, the blood sugar level usually normalizes again.

What forms of glucose tolerance test are there?

There are two forms of the glucose tolerance test: a short version, the so-called glucose challenge test, and a full glucose tolerance test. The short version is less expensive and serves as a preliminary test to determine risk for diabetes or gestational diabetes. Both tests are often called merely sugar testing.

Glucose Challenge Test

The glucose challenge test is a short version of the sugar test. The test can be done at any time of the day. To do this, drink a large glass of concentrated sugar solution: 50 g of glucose (glucose) dissolved in 250 to 300 ml of water. After one hour, blood is drawn to determine the level of blood sugar.

Glucose tolerance test

For the glucose tolerance test, it is essential to come to the doctor’s office in the morning with an empty stomach. Sober means you did not have breakfast and had your last meal the night before. This also applies to drinks except for water.

For the test, blood is first taken to determine to fast blood sugar. The blood is extracted from the vein, the fingertip or the earlobe. Then you drink a large glass of concentrated sugar solution. In the glucose tolerance test, 75 g of glucose is dissolved in 250 to 300 ml of water. For children, the amount is calculated according to body weight. If it is necessary to clarify a suspected diabetes mellitus after two hours blood is again taken and the blood sugar is measured. If gestational diabetes is suspected, blood will be considered one hour after the first test and then again after two hours.

It is recommended that you perform the test while lying or sitting and not eating, drinking or smoking until the last time you take your blood. It is essential to eat a healthy and balanced diet in the days before the test. Substantial changes in the usual food, such as a diet, can influence the outcome of the trial and weaken its meaning. Certain medications can also distort the result. What exactly should be considered, everyone can discuss in advance with the doctor.

What does “sobering” mean?

Sometimes it is essential to go to a specific exam soberly or not to take a medication directly after eating. Being “sober” means the stomach will be empty after a particular time. However, when should you give up solid food? Moreover, what about drinks?


Treatments and examinations: If you want to go to the clinic sober in the morning or if you have an operation in front of you, you usually take the last meal the evening before and you can not have breakfast. After the last meal is still a small snack like pretzel sticks or an apple in order. At least the last six to eight hours before the examination or surgery begins, you should not eat anything at all. When it comes to the stomach or intestines, it may also be necessary to eat for a long time. It would help if you also refrained from smoking before surgery.

Medicines: If you take drugs on an empty stomach, it usually does not mean you have to give up on a meal. Instead, they are made before having breakfast, lunch or dinner. Of course, you can wash down the medicine with a sip of water. It usually suffices to wait at least 30 minutes to start eating.


Treatments and examinations: From when nothing should be drunk, depends on the respective treatment or testing. While early as the last meal usually takes no carbonated drinks or dairy products, more to a glass of clear water is still problematic even two to three hours before the examination or treatment often.
Medications: Medications are often taken with a glass of water, even if you otherwise should stay sober before taking. In any case, water is best: taking certain medicines with milk or fruit juices may affect their effects.

In which examinations or treatments must one be sober?

Being sober is sometimes necessary for a variety of reasons, such as having medications work as intended, or because the stomach needs to be empty for it to be examined. In particular, during the following treatments and examinations it may be necessary to abstain from eating and drinking for a specific time:

Blood tests

Investigations with contrast agents such as computed tomography
Some ultrasounds of the abdomen
Stress tests in case of suspected food intolerances
Endoscopies such as gastroscopy
Surgery under anesthesia
Taking certain medications

Since it depends on the particular treatment or examination, exactly when someone should abstain from eating and drinking, it is essential to discuss this with the doctor. More information on whether it is necessary to be sober can also be found in the leaflet of medication and the scans for examinations and operations. If you are unsure, you can get advice in the doctor’s office or the pharmacy.


Leave a Reply