Overview

Purpose:

• The 2.5-hour glucose tolerance test is used to diagnose diabetes or impaired glucose tolerance, particularly in cases where the standard 3-hour test may not be applicable or where shorter tests are preferred.

Procedure:

1. Preparation: You will need to fast for at least 8-12 hours before the test, consuming only water.
2. Initial Blood Draw: A fasting blood glucose sample is taken.
3. Glucose Drink: You will drink a glucose solution, typically containing 75 grams of glucose.
4. Subsequent Blood Draws: Blood samples are taken at 30 minutes, 1 hour, and 2.5 hours after consuming the glucose solution.

Risk Assessment

• Diabetes Risk: Elevated glucose levels at multiple time points can indicate the presence of diabetes.
• Gestational Diabetes: Pregnant women at risk or with symptoms might be tested, especially if there are risk factors like obesity or a family history of diabetes.

Normal Range

• Fasting: Less than 95 mg/dL (5.3 mmol/L)
• 30 minutes: Less than 140 mg/dL (7.8 mmol/L) — Note: This specific timing might not be used in all protocols, but it’s included here for context.
• 1-hour: Less than 180 mg/dL (10.0 mmol/L)
• 2.5-hour: Less than 140 mg/dL (7.8 mmol/L)

Interpretation

• Normal: Blood glucose levels rise after drinking the glucose solution but return to normal within 2.5 hours.
• Impaired Glucose Tolerance (IGT): Glucose levels are higher than normal at one or more intervals but not high enough to meet the criteria for diabetes.
• Diabetes: Criteria for diagnosing diabetes may include:
  • Fasting glucose ≥ 95 mg/dL (5.3 mmol/L)
  • 1-hour glucose ≥ 180 mg/dL (10.0 mmol/L)
  • 2.5-hour glucose ≥ 140 mg/dL (7.8 mmol/L)

Sample Type

• Blood Samples: Blood is drawn from a vein in your arm at the fasting state, and then again at 1 hour and 2.5 hours after consuming the glucose drink.