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Glucose Tolerance Test (GTT)

Requirements prior to the test

  • You are to remain on a normal, unrestricted diet for at least 3 days prior to the test.
  • You have had no significant illness for 2 weeks prior to test.
  • Fasting is required for a period of 10-12 hours prior to the test - no food or fluids such as tea, coffee, or fruit juice. You may have sips of water if you are thirsty.
  • Due to the nature of the test, testing is generally done in the morning.
  • Certain centres will require you to make an appointment; please telephone your chosen collection centre to check. 
  • Maintain normal activity prior to the test.
  • Avoid smoking for one hour before and during the test.
  • Before drinking the glucose, please inform the collection staff if you have any allergies.

What to do during the procedure

  • You must remain seated quietly during the test. 
  • You will be at the collection centre for a minimum of 2 hours. 
  • You are required to remain in the collection centre until the procedure is completed.
  • Bring some reading material or other activity to pass the time.
  • If you feel unwell during the test, please inform the collection staff, as you may wish to lie down.

What the procedure involves

  • Collection of a fasting blood sample.
  • Drinking a 75g bottle of glucose within 5 minutes.
  • Collection of a blood sample 1 hour after consuming glucose. 
  • Collection of a blood sample 2 hours after consuming glucose.

Note: If insulin levels are requested with the GTT, the collection staff will draw blood for this using a separate tube, at the same time as each glucose blood sample is collected.

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