Knowledge base

What does OGTT mean?

The oral glucose tolerance test (also known as OGTT) is used to screen for diabetes that does not yet cause symptoms, as well as prediabetic conditions (impaired glucose tolerance, insulin resistance) and gestational diabetes.

What does the oral glucose tolerance test show, and why is it important to perform it?

In Hungary today, 68% of the adult population is overweight or obese, which poses a significant risk for type 2 diabetes and cardiovascular diseases.

Diabetes is the leading cause of blindness, end-stage renal failure, and non-traumatic limb amputations in our country today.

The treatment of the disease and its complications places a heavy burden on the patient, their family, the healthcare system, and society as a whole. In Hungary, even 15 years ago, the annual cost of treating diabetes complications was 17 billion forints, with the total societal cost nearing 100 billion forints. This is why it is crucial to detect the disease as early as possible. According to the results of a recent representative survey in Hungary, the prevalence of diabetes in the 20-69 age group is 7.5%, but without screening, half of the cases go undetected. Yet, diabetes diagnosed at the age of 40 can result in a loss of 10-15 years of quality life!

Pregnancy

Another important population at risk for diabetes is pregnant women. Diabetes diagnosed during pregnancy is known as gestational diabetes (GDM). The method for screening GDM is the OGTT test, conducted between the 24th and 28th weeks of pregnancy. According to data from Hungarian centers, the prevalence of GDM is 5-10%. Moreover, 50% of mothers with GDM develop “true” diabetes within 5 years after childbirth!

Carbohydrate metabolism disorder

Carbohydrate metabolism disorders that precede manifest diabetes—such as impaired fasting glucose (IFG) and impaired glucose tolerance (IGT)—also pose a significant cardiovascular risk. According to international data, the prevalence of IFG in the adult population averages between 4.8-7.6%, while the prevalence of IGT ranges from 3-9%. Screening experiences show that for every known diabetic, there is one undiagnosed diabetic individual. Applying this international data to the Hungarian population, approximately 1-1.5 million people in Hungary are diabetic, and there is an almost equal number of individuals in the early stages of carbohydrate metabolism disorders (prediabetics). A study involving a population of seventy thousand people aged 20-70 (FINDRISC Hungary) revealed that 7.6% of high-risk individuals who were previously unaware of their carbohydrate metabolism disorder (!) were already manifest diabetics at the time of the study, 14.08% had IFG, and an astonishing 24.79% had IGT. In 46% of the participants who underwent the oral glucose tolerance test, a previously undiagnosed carbohydrate metabolism disorder was found!

Screening large populations would aid in the early detection of carbohydrate metabolism disorders. In cases of slightly elevated fasting blood glucose levels (≥5.6 mmol/l), it is already recommended to perform a 75 g glucose OGTT.

When is it recommended to perform an oral glucose tolerance test (OGTT)?

To rule out gestational diabetes, the OGTT should be performed between the 24th and 28th weeks of pregnancy in all cases or based on the attending physician’s instructions.

For individuals with a family history of carbohydrate metabolism disorders, such as diabetes or insulin resistance.

At the discretion of the attending physician, the test is recommended in any case where a carbohydrate metabolism disorder is suspected, based on the following symptoms and complaints:
– Weight loss or gain
– Increased thirst
– Frequent sugar cravings during the day
– Irregular menstruation
– PCOS (polycystic ovary syndrome)
– Difficulty conceiving
– Extreme mood swings, fatigue, and concentration issues related to meals
– Abnormal fasting blood glucose levels
– Slow wound healing
– Excessive urination
– Suspected insulin resistance

It is also essential for monitoring the treatment of an already diagnosed condition.

The procedure of the test.

1. Preparation
In the 3 days leading up to the test, a diet containing at least 150 grams of carbohydrates per day is required (foods high in carbohydrates include bread, pasta, milk chocolate, bananas, rice, potatoes, etc.). Exhaustive physical activities, such as cardio workouts, should be avoided.

The night before the test, or at least 8-10 hours prior, you should not eat or drink anything (except still water). This ensures that your blood glucose level is as close to normal as possible at the start of the test.

2. First blood draw
On the day of the test, you must arrive at the doctor’s office or laboratory on an empty stomach. The doctor or lab assistant will perform the first blood draw to check your fasting blood glucose level.

3. Glucose drink consumption
After the first blood sample is taken, within a few minutes, you will need to drink a solution containing 75 grams of glucose. An alternative to this unpleasant-tasting solution is the GERO-DEX glucose drink.

4. Waiting period
After consuming the glucose drink, depending on the type of test, you will need to wait for a set period, such as 2 hours for the 2-point test. During this time, it is important that you do not eat, drink (except water, if permitted), smoke, or engage in intense physical activity, as these can affect the test results.

5. Additional blood draws
During or at the end of the waiting period, additional blood samples will be taken. Typically, blood draws are done at 1 and 2 hours to see how your blood glucose levels change after consuming the glucose drink.

6. Results evaluation
The doctor will evaluate the changes in your blood glucose levels based on the fasting and post-load blood samples. These results will help determine how your body processes sugar and whether diabetes or prediabetes is present.

Factors that could influence the test results, such as infections, medication effects, menstruation, etc., should be considered, and in some cases, it may be necessary to postpone the glucose tolerance test.