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Glucose tolerance test

Known as: Glucose tolerance test
SKU: 1909


Study material: Venous blood
Response time (working day): 1
The test is done on an empty stomach: Yes
Home call service: Yes
Country: Georgia

General Information

After oral administration of large amounts of glucose in healthy subjects, insulin is released immediately and reaches a maximum after about 30-60 minutes. When we have enough insulin to metabolize glucose at the beginning of the test, glucose levels return to normal in about 3 hours.

Insufficient secretion of insulin or peripheral insulin resistance will lead to a significant increase in blood glucose.

When determining basal (fasting) or postprandial blood glucose, the test can confirm or deny the diagnostics of diabetes.

When should we take the test?

  • Fasting blood sugar>> 126 mg / dL (> = 6,99 mmol / L);
  • Family history of diabetes;
  • Obesity;
  • History of recurrent infections (skin or urinary tract infections);
  • Unexplained episodes of hypoglycemia;
  • Patients with miscarriages, premature births, stillbirths, or macrosomias;
  • Transient glycosuria or hyperglycemia during pregnancy after surgery, trauma, stress, or myocardial infarction.

Test contraindications

  • Patients with recurrent hypokalemic paralysis;
  • Basal hyperglycemia (≥ 126 mg / dL);
  • Persistently normal basal values ​​of blood glucose;
  • Postprandial blood glucose ≥200 mg / dL;
  • Clinically pronounced diabetes;
  • Secondary diabetes (e.g. after taking hormone).

How is the test conducted?

Adults: 75 g of glucose dissolved in cold water should be drunk for 5 minutes.

Children: The amount of glucose depends on the patient's weight: 1,75 g / kg body weight - maximum 75 g.

Two blood samples will be taken: directly before glucose injection and 120 minutes after.

In certain clinical situations, at the request of the physician, several samples may be taken: 30, 60, 90, 120, 180 minutes.

Side effects: Some people may have nausea or vagal symptoms during the test.

Possible interpretation of the results

Interpretation of basal blood glucose values ​​and glucose tolerance test is performed according to ADA (American Diabetes Association) criteria:

Normoglycemia Conditions associated with an increased risk of diabetes Diabetes mellitus
Basal glucose in the blood   <100 mg / dL (<5,6 mmol / L)   100-126 mg/dL (5.6-6.9 mmol/L) 126 mg / dl
Blood glucose, 75 hours after ingestion of 2 g of glucose <140 mg / dl  140-200 mg / dL (7.8-11.1 mmol / L) (for intolerant glucose)  ≥200 mg / dL (≥11.1 mmol / L)

At least two abnormal glucose tolerance tests are required to diagnose diabetes.

The glucose tolerance test is useful not only for diagnosing diabetes but also for identifying patients with impaired glucose tolerance (IGT).

People with IFG (increased glucose tolerance) as well as individuals with IGT are part of an intermediate group who, although they do not meet the diagnostic criteria for diabetes, have too high a glucose level to be considered normal. These people were previously considered to have prediabetes, but according to the new ADA (2010) recommendations, IFG and IGT should not be considered as independent clinical units, but as high-risk categories in the development of diabetes and cardiovascular disease. IFG and IGT are associated with obesity (especially in the abdomen), high blood pressure, and dyslipidemia (high triglycerides and low HDL-cholesterol). Increased physical activity, weight loss, and the intake of certain pharmacological agents prevent or slow down the development of diabetes in people with glucose intolerance.

Other clinical conditions related to glucose tolerance:

  • Decreased glucose tolerance may occur with high blood sugar: postgastrectomy, excessive glucose uptake, type III, IV and V hyperlipidemia, hemochromatosis, Cushing's disease, CNS damage.
  • Decreased glucose tolerance with hypoglycemia may occur: von Gierke's disease, severe liver disease, elevated epinephrine levels.
  • Increased glucose tolerance with a flattened curve (obtained from blood glucose readings 30, 60, 90, 120, 180 min) may occur: Hyperplasia or pancreatic islet cell carcinoma, malabsorption (Sprue, celiac disease, Whipple disease), Addison's disease, Hippo's disease, Hypo Liver disease.

Diagnostic limitations

The test has limited relevance in the diagnostics of diabetes in children and is rarely used for this purpose.

  • Smoking can increase glucose levels.
  • A modified diet (eg weight loss regimen) can lower glucose tolerance and lead to "false diabetes".
  • Infectious diseases and surgery can affect glucose tolerance, so testing is recommended within 2 weeks of an acute episode.
  • Other pathological conditions that can lead to false pathological results during the glucose tolerance test: duodenal ulcer, gastrectomy, hypokalemia, hypermagnesemia.

Additional information


How to prepare for the test?

  • It is advisable to fast (at least 8 hours (not more than 16 hours) after consuming any calories);
  • Small amounts of water are allowed;
  • The patient should be fed normally for the last 72 hours (abstinence from> 150 g of carbohydrates and alcohol per day);
  • Smoking and physical activity are prohibited during the test.


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