A glucose tolerance test helps in the diagnosis of diabetes and should be included for those who are at risk for diabetes. For those who have already been diagnosed with diabetes a glucose tolerance test is not needed. If repeated studies show a slight increase or normal blood sugar in combination with episodic glycosuria, or if there are any other doubts about the diagnosis, a glucose tolerance test (GTT) is performed.
Any, even accidental, single detection of hyperglycemia or glycosuria requires careful examination to exclude or confirm diabetes.
Impaired glucose tolerance. A glucose tolerance test is used to diagnose impaired glucose tolerance.
Method for glucose tolerance test
For at least 3 days prior to the test, those getting checked must comply with normal diet and physical activity.
The glucose tolerance test should be carried out in a calm state, it should not be preceded by stressful situations or inadequate conditions. The usual glucose tolerance test involves the collection of capillary (mixed) blood from a finger. The first sample is taken in the morning on an empty stomach after a night fast of 10-14 hours (water intake is allowed). During the study, the patient should sit quietly (or lie down), smoking, physical activity is not allowed. On the eve and on the day of the study of medicines, all sorts of procedures should be canceled. Glucose tolerance test is not recommended during menstruation. During pregnancy, a glucose tolerance test may not be indicative.
After the first blood sampling from a finger, the subject takes in 75 g of glucose in 250-500 ml of water for 2-5 minutes. To improve the taste of drinking (and prevent nausea in some), you can add lemon juice or citric acid.
Any, even accidental, single detection of hyperglycemia or glycosuria requires careful examination to exclude or confirm diabetes.
When conducting a test in obese individuals, glucose is added at the rate of 1 g per 1 kg of body weight but not more than 100 g. After glucose is taken, blood for sugar is taken at intervals of 30 minutes for 2 hours. To obtain sufficient information, you can limit yourself to repeated blood sampling 1 and 2 hours after glucose intake, since these periods are most indicative of characterizing the functional state of the pancreas and insulin production.
Sometimes, after a glucose tolerance test, flattened sugar curves are observed, in which there is a slight increase in glycemia after glucose intake. They can be considered as a variant of the norm. However, if a patient has a flattened sugar curve combined with episodic, clinically pronounced hypoglycemia, gastrointestinal disturbances, it should be interpreted as an indicator of hypoglycemia, impaired glucose absorption or impaired glucose tolerance. When interpreting a glucose tolerance test, attention should be paid to age-related features. It is accepted that in people over 50 years of age, the glucose tolerance test at the 1st and 2nd hour rises by an average of 0.5 mmol / l (10 mg%) every next 10 years. In order to correct the glucose tolerance test in people over the age of 50, for every 10 years, glycemia at the 1st and 2nd hour should be added to 0.5 (in mmol / l) or 10 (in mg%).
When interpreting a glucose tolerance test, attention should be paid to age-related features, pregnancy and endocrine diseases.
The glucose tolerance test is influenced by many factors that must be taken into account when diagnosing diabetes mellitus. These include prolonged bed rest, infections and fevers, diseases of the digestive tract with impaired glucose absorption, malignant tumors, medications (adrenaline, caffeine, diuretics, morphine, diphenan, psychotropic drugs and antidepressants).
Glucose tolerance disorders are often found in various endocrine diseases: acromegaly, Cushing’s disease, thyrotoxicosis, and others. They develop with renal failure and cirrhosis. Pregnancy may be accompanied by a slight decrease in carbohydrate tolerance (more often the blood sugar level rises 2 hours after glucose loading).