Impaired Glucose Tolerance (IGT) – Guide for primary care clinicians

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  The Oral Glucose Tolerance Test (OGTT) is a diagnostic test used to assess how the body processes glucose, particularly to diagnose Impaired Glucose Tolerance (IGT), prediabetes, or diabetes.

  
  

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• IGT is a pre-diabetic state with ↑ risk of progressing to Type 2 Diabetes Mellitus (T2DM).

• Often asymptomatic, but associated with insulin resistance, especially in muscle tissue.

• Linked to ↑ risk of cardiovascular disease (CVD), even without progression to T2DM

OGTT Procedure (Oral Glucose Tolerance Test)

Preparation

• Fast for 8–12 hours (water only allowed).

• Avoid:

  • Smoking

  • Intense physical activity

  • Medications that affect glucose (e.g., steroids )

Step-by-Step Process

1. Baseline Sample

   • Take fasting venous blood sample → measure fasting plasma glucose.

2. Glucose Load

   • Patient drinks 75g glucose dissolved in water

   • Must be consumed within 5 minutes

3. Waiting Period (2 hrs)

   • Patient rests quietly

   • No food, drink (except water), or physical activity

4. 2-Hour Sample

   • Second venous blood sample taken exactly 2 hours after glucose intake

   • Measure 2-hour plasma glucose

📋 Definition of Impaired Glucose Tolerance (WHO/ADA)

Interpretation of OGTT (WHO Criteria)...