Glucose Tolerance Test

Glucose Tolerance Test

The Glucose Tolerance Test (GTT) is a diagnostic tool used to evaluate how well the body processes glucose.

Process and Method

1. Preparation:

   • The patient is advised to maintain a normal carbohydrate diet (at least 150g/day) for 3 days before the test.

   • Fasting for 8-12 hours is required before the test, with only water allowed.

2. Procedure:

   • Baseline Measurement: A fasting blood sample is taken to establish a reference glucose level.

   • Glucose Administration: The patient consumes a glucose solution (usually 75g dissolved in water for adults).

   • Subsequent Blood Draws: Blood samples are collected at regular intervals (e.g., every 30 minutes for 2-3 hours) to monitor glucose levels.

   • Analysis: The blood glucose levels are plotted on a graph to observe the body's response.

3. Graphical Representation:

   • The graph typically shows time on the x-axis and blood glucose levels on the y-axis.

   • A normal response shows a peak in glucose levels followed by a return to baseline within 2 hours.

   • Abnormal responses (e.g., delayed return to baseline) may indicate conditions like diabetes or impaired glucose tolerance.

Clinical Applications

1. Diabetes Diagnosis:

   • GTT is commonly used to diagnose Type 2 diabetes, prediabetes, and gestational diabetes.

   • It helps identify insulin resistance and impaired beta-cell function.

2. Gestational Diabetes:

   • Pregnant women are often screened using a modified GTT to detect gestational diabetes, typically between 24-28 weeks of pregnancy.

3. Rare Conditions:

   • GTT can help diagnose reactive hypoglycemia, acromegaly, and other carbohydrate metabolism disorders.

4. Research and Monitoring:

   • It is used in research settings to study glucose metabolism and in clinical practice to monitor the effectiveness of diabetes treatments.

Graphical Representation:

1. Normal Glucose Tolerance Curve:

   • After consuming glucose, blood sugar levels rise and peak within 30–60 minutes.

   • The levels then gradually return to baseline within 2 hours.

2. Impaired Glucose Tolerance Curve:

   • Blood sugar levels rise higher than normal and take longer to return to baseline.

   • This indicates a reduced ability to process glucose efficiently.

3. Diabetic Glucose Tolerance Curve:

   • Blood sugar levels rise significantly higher and remain elevated beyond 2 hours.

   • This is a hallmark of diabetes.

Insights into Interpreting Results:

• Fasting Blood Glucose:

  • Normal: <92 mg/dL

  • Impaired: 92–125 mg/dL

  • Diabetic: ≥126 mg/dL

• 2-Hour Blood Glucose:

  • Normal: <140 mg/dL

  • Impaired: 140–199 mg/dL

  • Diabetic: ≥200 mg/dL

These curves and thresholds help clinicians diagnose conditions like diabetes, prediabetes, and gestational diabetes.