Glucose tolerance test

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Glucose tolerance test

A glucose tolerance test (GTT) is a medical test used to diagnose diabetes mellitus, insulin resistance, and other disorders of carbohydrate metabolism. The test measures the body's ability to metabolize glucose, the primary source of energy for cells.

Types of Glucose Tolerance Tests

There are several types of glucose tolerance tests, including:

• Oral Glucose Tolerance Test (OGTT): This is the most common type of GTT. It involves fasting overnight and then drinking a glucose solution. Blood samples are taken at various intervals to measure blood glucose levels.
• Intravenous Glucose Tolerance Test (IVGTT): In this test, glucose is administered directly into the bloodstream through an intravenous line. Blood samples are taken to measure how quickly glucose is cleared from the blood.
• Gestational Glucose Tolerance Test: This test is used to diagnose gestational diabetes in pregnant women. It is similar to the OGTT but may involve different glucose concentrations and testing intervals.

Procedure

The procedure for an oral glucose tolerance test typically involves the following steps:

1. **Preparation**: The patient is instructed to fast for at least 8 hours before the test. Water is usually allowed. 2. **Baseline Measurement**: A blood sample is taken to measure fasting blood glucose levels. 3. **Glucose Administration**: The patient drinks a glucose solution, usually containing 75 grams of glucose. 4. **Blood Sampling**: Blood samples are taken at specific intervals, typically at 30 minutes, 1 hour, 2 hours, and sometimes 3 hours after drinking the glucose solution. 5. **Analysis**: The blood samples are analyzed to measure glucose levels and assess how well the body processes glucose.

Interpretation of Results

The results of a glucose tolerance test are interpreted based on the blood glucose levels measured at different time points. The following criteria are commonly used:

• **Normal**: Fasting blood glucose < 100 mg/dL; 2-hour blood glucose < 140 mg/dL.
• **Impaired Glucose Tolerance (IGT)**: Fasting blood glucose 100-125 mg/dL; 2-hour blood glucose 140-199 mg/dL.
• **Diabetes Mellitus**: Fasting blood glucose ≥ 126 mg/dL; 2-hour blood glucose ≥ 200 mg/dL.

Clinical Significance

The glucose tolerance test is an important tool in the diagnosis and management of diabetes and other metabolic disorders. It helps identify individuals at risk for developing diabetes and allows for early intervention and management.

Related Tests

• Fasting blood sugar
• Hemoglobin A1c
• Random blood sugar

See Also

• Diabetes mellitus
• Insulin resistance
• Gestational diabetes
• Carbohydrate metabolism