Glucose tolerance test (glucose fasting, 1 hour and 2 hours after exercise)

Indications for the test

The test is indicated for identifying hidden forms of diabetes in the presence of risk factors:

• Metabolic disorders: excess body weight, poor nutrition with a predominance of foods rich in refined sugar, lack of physical activity.
• Endocrine pathology: diseases of the thyroid gland, adrenal glands, pituitary gland.
• Liver diseases.
• Pregnancy diabetes.
• Impaired glucose tolerance.
• Genetic predisposition (presence of first-degree relatives with diabetes).

When is a glucose tolerance test prescribed?

The test is prescribed to patients at high risk for diabetes. This group includes:

• suffering from excess weight, arterial hypertension, heart and vascular diseases,
• having close relatives with diabetes,
• leading a sedentary lifestyle,
• patients who had hyperglycemia in a stressful situation (during pneumonia, heart attack, stroke).

In pregnant women, risk factors are:

• BMI is more than 30,
• history of birth of a child weighing more than 4.5 kg,
• history of polycystic ovary syndrome,
• having close relatives with diabetes,
• development of gestational diabetes in previous pregnancies.

GTT is not advisable for patients who have identified laboratory signs of diabetes mellitus (blood glucose level over 7.0 mmol/l).

Carrying out the test

1. GTT is carried out in the morning on an empty stomach (after 8-12 hours of fasting).
2. Before performing the Glucose Tolerance Test, capillary blood (from a finger) must be taken and the fasting glucose level is determined using a glucometer.
3. If the fasting glucose level is 7.0 mmol/L or higher, the glucose tolerance test will NOT be performed.
4. In other cases, the first sample of venous blood is taken (on an empty stomach), then it is necessary to take a carbohydrate load: 75 g of glucose dissolved in 200-300 ml of water (glucose, water, glass are provided in the laboratory). After taking a carbohydrate load, physical activity is limited, you must sit quietly, you are not allowed to smoke or eat, you are allowed to drink water. You cannot replace glucose with sugar when performing a glucose tolerance test.
5. One hour later, a second venous blood sample is taken (1 hour after exercise). After this, physical activity is also limited, you must sit quietly, you are not allowed to smoke or eat, and you are allowed to drink water.
6. One hour later (and two hours after the start of the test), a second venous blood sample is taken (2 hours after the load).

An oral glucose tolerance test consists of determining the level of plasma glucose on an empty stomach and 2 hours after a carbohydrate load in order to diagnose various disorders of carbohydrate metabolism (diabetes mellitus, impaired glucose tolerance, fasting glycemia).

The research results are provided with a free doctor’s commentary.

Synonyms Russian

Oral glucose tolerance test (OGTT), a test for glucose tolerance, a test with 75 grams of glucose.

English synonyms

Glucose tolerance test (GTT), oral glucose tolerance test (OGTT).

Research method

Enzymatic UV method (hexokinase).

Units

mmol/l.

What biomaterial can be used for research?

Venous blood.

How to properly prepare for research?

• An oral glucose tolerance test should be performed in the morning after at least 3 days of unrestricted nutrition (more than 150 g of carbohydrates per day) and normal physical activity. The test should be preceded by an overnight fast for 8-14 hours (you can drink water).
• Your last evening meal should contain 30-50 grams of carbohydrates.
• Do not drink alcohol 10-15 hours before the test.
• Do not smoke the night before the test and until it is over.

General information about the study

An oral glucose tolerance test should be performed in the morning after at least 3 days of unrestricted nutrition (more than 150 g of carbohydrates per day) and normal physical activity. The test should be preceded by an overnight fast for 8-14 hours (you can drink water). The last evening meal should contain 30-50 g of carbohydrates. Do not smoke the night before the test and until it is over. After taking blood on an empty stomach, the subject should drink 75 g of anhydrous glucose or 82.5 g of glucose monohydrate dissolved in 250-300 ml of water within no more than 5 minutes. For children, the load is 1.75 g of anhydrous glucose (or 1.925 g of glucose monohydrate) per kg of body weight, but not more than 75 g (82.5 g); for children weighing 43 kg or more, the usual dose (75 g) is given. Smoking and vigorous physical activity are not allowed during the test. After 2 hours, blood is taken again.

It should be remembered that if the fasting blood glucose level exceeds 7.0 mmol/l, then the oral glucose tolerance test is not performed, since this blood glucose level itself is one of the criteria for diagnosing diabetes mellitus.

An oral glucose tolerance test allows you to diagnose various disorders of carbohydrate metabolism, such as diabetes mellitus, impaired glucose tolerance, fasting glycemia, but cannot clarify the type and causes of diabetes mellitus, and therefore, after receiving any result of an oral glucose tolerance test, it is advisable to conduct a mandatory consultation endocrinologist.

What is the research used for?

For diagnostics:

• diabetes mellitus;
• impaired glucose tolerance;
• fasting glycemia.

When is the study scheduled?

• In case of questionable glycemic values, to clarify the state of carbohydrate metabolism;
• when examining patients with risk factors for developing diabetes mellitus: age over 45 years;
• BMI more than 25 kg/m2;
• family history of diabetes (parents or siblings with type 2 diabetes);
• habitually low physical activity;
• presence of fasting glucose or a history of impaired glucose tolerance;
• gestational diabetes mellitus or a history of birth of a fetus weighing more than 4.5 kg;
• arterial hypertension (of any etiology);
• lipid metabolism disorder (HDL level below 0.9 mmol/l and/or triglyceride level above 2.82 mmol/l);
• the presence of any disease of the cardiovascular system.

When is it appropriate to perform an oral glucose tolerance test to screen for carbohydrate metabolism disorders?

When should an oral glucose tolerance test not be performed?

• Against the background of any acute disease, including infectious.
• While taking medications that increase glycemic levels (glucocorticoids, thyroid hormones, thiazides, beta blockers, oral contraceptives). Cancellation is required (according to doctor's recommendations) 3 days before the test.

What do the results mean?

Reference values

Performed at two time points, reference values ​​of glucose in the blood plasma for each point in the study results are given in accordance with the “Algorithms for specialized medical care for patients with diabetes mellitus” (2017):

Criteria for determining impaired fasting glycemia, impaired glucose tolerance and diabetes during GTT

Reasons for increased blood glucose levels:

• various disorders of carbohydrate metabolism (diabetes mellitus, impaired glucose tolerance, fasting glycemia);
• false positive result - a recent or ongoing acute illness, surgery or any other stressful situation, taking medications that increase glycemic levels (glucocorticoids, thyroid hormones, thiazides, beta blockers, oral contraceptives).

Reasons for low blood plasma glucose levels:

• taking medications that reduce glycemic levels (insulin, various sugar-lowering drugs);
• insulinoma;
• excessive fasting;
• intense physical activity on the eve of the test.

Prediabetic condition: causes

The main causes of impaired glucose tolerance are the following:

• significant excess weight, in the development of which the main factors are transmission and a sedentary lifestyle;
• genetic predisposition: it has been proven that family members where someone had or is suffering from diabetes are also at risk, which made it possible to identify certain genes responsible for the production of complete insulin, the sensitivity of peripheral tissue receptors to insulin and other factors;
• age and gender: most often prediabetes and diabetes are diagnosed in women over 45 years of age;
• other diseases: we are talking primarily about diseases of the endocrine system, leading to hormonal imbalance and metabolic failure, as well as diseases of the gastrointestinal tract (stomach ulcers, due to which the process of glucose absorption can be disrupted) and diseases of the cardiovascular system (atherosclerosis, high blood pressure, high cholesterol, etc.). For women, polycystic ovary syndrome may be a risk factor;
• complicated pregnancy: often prediabetes, which turns into type 2 diabetes, also occurs after gestational diabetes, which appears in women during pregnancy. Typically, problems with blood sugar levels occur in late pregnancy or large fetal sizes.

It should also be remembered that prediabetic condition can be diagnosed not only in adults, but also in children. Prediabetes in a child usually occurs as a consequence of an infectious disease, or, less commonly, of surgical intervention, which makes it necessary to pay special attention to the period of rehabilitation of the child after illness or surgery.

Prediabetic state: complications

The main complication of this condition is, of course, its possible transition to acquired type 2 diabetes, which is much more difficult to keep under control. In addition, the presence of excess sugar in the blood, even if not at a critical level, leads to an increase in blood density, which can cause the formation of plaques, blockage of blood vessels and, as a result, problems with the cardiovascular system, namely heart attacks and strokes.

In turn, the transition of the prediabetic state to diabetes entails possible damage to other body systems, including the kidneys, vision, nervous system, decreased immunity and general body resistance.

How to prepare for the glucose tolerance test

• 3 days before the analysis, it is important to adhere to your usual activity and usual diet without limiting the amount of carbohydrates (daily intake of more than 150 g of carbohydrates).
• The last dinner before analysis should contain 30–50 g of carbohydrates.
• The duration of the fasting period before the test should be from 8 to 14 hours (including overnight). Drinking water is allowed.
• On the eve of the procedure, as well as on the day of the study until its completion, it is not recommended to smoke or drink alcohol.
• Before starting OGTT, the initial fasting blood glucose concentration is assessed.

If the indicator goes beyond the norm, the test will be canceled due to inappropriateness and unsafety.

Glucose - chemistry and anatomy

Glucose is present in fruits and vegetables.

Glucose is a monosaccharide that is present in fruits and vegetables. Historical name: "grape sugar". In appearance it is a white crystalline powder with a sweet taste.

When paired with another monosaccharide, fructose forms a well-known and widely consumed sugar. In addition, glucose is part of many complex carbohydrates.

This monosaccharide is a universal source of energy for plants, animals, and humans. It ensures metabolic processes in the body. It is the increase in the level of this sugar in the blood that provides a person with a feeling of fullness after eating.

So they ate candy - a fast carbohydrate - glucose rushed into the blood. I don't want to eat. For a while. Then everything repeats again. My sugar level dropped and I wanted to eat. You ate and feel good. But all processes in the body must be in balance. Including the rate of absorption and processing of carbohydrates. The pancreas regulates the processes of glucose absorption.

It is the largest endocrine gland in the human body. The organ produces the hormone insulin, which ensures the normal breakdown and absorption of grape sugar. But, according to statistics, people have sharply increased their consumption of carbohydrates over the past 20 years. Let's add stress and unfavorable environmental conditions. The load on the pancreas increases and at some point a failure may occur.

How much glucose should there be in the blood? Find out from the video:

https://www.youtube.com/watch?v=Eqrg24QtnA0

Contraindications

Contraindications to the study may be the presence of the following diseases in patients:

• congenital or acquired glucose intolerance;
• inflammatory diseases or viral respiratory infections (even a runny nose);
• gastrointestinal diseases.

The test is contraindicated if the patient is in the rehabilitation period after surgery or is being treated with glucocorticosteroids (as they can increase glucose levels).

Pregnant women may refuse to take the test if they:

• severe toxicosis;
• risk of miscarriage;
• pregnancy is more than 32 weeks (since performing a test during this period can be dangerous for the fetus).

How to prepare

It is necessary to take into account the influence of many factors, since the test itself is quite capricious. Subjects should refrain from coffee and should not drink alcoholic beverages during the day before the diagnosis. It is also necessary to avoid smoking.

Patients should eat moderately (the amount of carbohydrates is 120-150 g per day), be sure to exclude intense physical activity and avoid dehydration.

Within 3 days before taking tests, it is not recommended to use drugs that can distort test results (corticosteroids, vitamin C, oral contraceptives and others).

During the second blood draw, you need to remain calm (relax, it’s better to sit down or lie down), otherwise the test may show false results.

The process of preparing for research in pregnant women is almost no different from that in other patients. It is important to follow the right regime and eat right. A woman should tell her doctor about taking the test while taking progesterone as well as beta-blocking medications.