Overview
The Oral Glucose Tolerance Test (OGTT) is a standardized diagnostic procedure used to evaluate glucose metabolism and diagnose diabetes mellitus, gestational diabetes, and other disorders of glucose homeostasis.
Required Materials
- 75g anhydrous glucose dissolved in 300mL water
- Venipuncture equipment
- Timer
- Blood collection tubes
- Patient identification labels
- Laboratory requisition forms
Patient Preparation
Pre-test Instructions
- Fast for 8-14 hours prior to test
- Maintain usual physical activity
- Continue normal diet (≥150g carbohydrates/day) for 3 days before test
- Avoid medications that affect glucose metabolism when possible
Contraindications
- Acute illness
- Recent surgery
- Active infection
- Severe morning sickness (in pregnancy)
Procedure Steps
1. Initial Assessment (0 minutes)
- Verify patient identity and fasting status
- Record baseline vital signs
- Collect fasting blood sample
2. Glucose Administration
- Administer 75g glucose solution
- Patient must consume within 5 minutes
- Record exact time of completion
3. Monitoring Period
- Patient remains seated
- No smoking, eating, or drinking
- Minimal physical activity
4. Blood Collection
- Draw blood at specified intervals:
- Fasting (0 min)
- 1 hour (60 min)
- 2 hours (120 min)
Result Interpretation
Standard 2-hour OGTT Criteria
Non-pregnant adults:
- Normal: <140 mg/dL
- Impaired: 140-199 mg/dL
- Diabetes: ≥200 mg/dL
Pregnancy (GDM):
- Fasting: ≤95 mg/dL
- 1 hour: ≤180 mg/dL
- 2 hour: ≤155 mg/dL
Documentation Requirements
- Test start/end times
- Glucose load administration time
- Blood draw times
- Patient tolerance
- Any protocol deviations
Quality Control
- Verify glucose solution preparation
- Confirm proper specimen handling
- Document temperature conditions
- Maintain chain of custody