Glucose Tolerance Test (GTT)

 The glucose tolerance test (GTT) aids in the diagnosis of diabetes mellitus. If the glucose levels peak at higher than normal at 1 and 2 hours after injection or ingestion of glucose and are slower than normal to return to fasting levels, then diabetes mellitus is confirmed.

Normal Lab Values for Glucose Tolerance Test (GTT)

  • 70 – 110 mg/dL (baseline fasting)
  • 110 – 170 mg/dL (30 minute fasting)
  • 120 – 170 mg/dL (60 minute fasting)
  • 100 – 140 mg/dL (90 minute fasting)
  • 70 – 120 mg/dL (120 minute fasting)

Nursing Considerations

  • Instruct the client to eat a high-carbohydrate (200 to 300 g) diet for 3 days before the test.
  • Instruct the client to avoid alcohol, coffee, and smoking for 36 hours before the test.
  • Instruct the client to avoid strenuous exercise for 8 hours before and after the test.
  • Instruct the client to fast for 10 to 16 hours before the test.
  • Instruct the client with diabetes mellitus to withhold morning insulin or oral hypoglycemic medication.
  • Instruct the client that the test may take 3 to 5 hours, requires IV or oral administration of glucose, and the taking of multiple blood samples.