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Glucose tolerance test (GTT)

Your doctor has requested that you have a glucose tolerance test. These tests are generally scheduled for first thing in the morning. This test will take around 2 hours to complete.

Three blood specimens will be taken unless your doctor has extended the test and asked for additional specimens to be taken.

NOTE: This test is not recommended for patients who have had gastric bypass or banding surgery.

Preparing for your test

Three days before the test continue with your usual diet and undertake your usual activities.

You will need to fast the evening before the test. From this time, do not eat or drink (water is permitted but do not drink tea, coffee, or cordial) until the test is finished the following day. Do not smoke during the fasting period.

Collecting your samples

Please inform the collecting staff if:

  • this is a repeat test because you were unable to tolerate the standard glucose drink on a previous occasion
  • during the testing period, you vomited or felt nauseous as this may affect the interpretation of test results.

Do not perform any physical exercise, smoke, eat or drink (except water) during the test.

  1. A fasting blood specimen is taken (specimen 1).
  2. You will then be given a 75g dose of glucose to drink, all of which is to be consumed within 5 minutes. Once you finish the drink you will be asked to stay in the waiting room.
  3. After 1 hour, another blood specimen is collected (specimen 2).
  4. A third blood specimen is collected 1 hour later (specimen 3).

After the test you are free to return to your usual activities and consume food and drink.

Contact the collection centre or your referring doctor if you have any questions about the glucose tolerance test.

Need more information?

Glucose tolerance test at Lab Tests online.

QIS document number: 23585

Last updated: 29 April 2020