glucose challenge (tolerance) test

Indications

• screen for gestational diabetes

• ref suggests GTT for diagnosis of dysautonomia & small fiber neuropathy in a 44 year old man with normal HgbA1c & fasting plasma glucose

Contraindications

• generally NOT recommended as a screening test for diabetes mellitus (except in the case of pregnancy) because of cost, incovenience, lack of reproducibility, & occasional patient discomfort

Adverse effects

• higher doses of glucose may cause nausea/vomiting & invalidate results
• see gestational diabetes

Clinical significance

Abnormal glucose tolerance test:

• fasting glucose > 115 mg/dL
• any value of glucose > 200 mg/dL
• 2 hour glucose > 140 mg/dL
  • a value > 200 mg/dL makes the diagnosis of diabetes mellitus
• gestational GTT (see gestational diabetes)
  • fasting glucose > 105 mg/dL
  • 1 hour glucose > 190 mg/dL
  • 2 hour glucose > 165 mg/dL
  • 3 hour glucose > 145 mg/dL

Procedure

• fasting serum glucose
  • between 7 & 9 AM
  • after 30 minutes of rest
• glucose ingestion
  • within 5 minutes of obtaining fasting serum glucose
  • consumed within a 5 minute interval
  • dose
    • adults: 75 g used
    • pediatrics: 1.75 g/kg
    • 50 g used for gestational screening
    • 100 g used for gestational GTT
• specimens drawn at 1 & 2 hours after glucose ingestion
• testing for gestational diabetes utilizes specimens drawn at 1,2 & 3 hours after glucose ingestion

More general terms

• provocative clinical test
• chemistry panel

More specific terms

• growth hormone (GH) suppression test; glucose challenge test for acromegaly

Additional terms

• diabetes mellitus type 2 (insulin-resistant)
• impaired fasting glucose
• impaired glucose tolerance
• pregnancy (gestation)