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Glucose Tolerance Test

Glucose Tolerance Test

The Glucose Tolerance Test (GTT) is a timed series of blood glucose measurements taken after a glucose load is taken by the patient. People with normal glucose metabolism will have a relatively modest rise in their blood sugar levels, whereas those with diabetes or impaired glucose tolerance will have a higher peak of their blood glucose levels.

How the Test is Performed

The Glucose Tolerance Test (GTT) is performed in the morning, after an 8 to 16 hour overnight fasting period. During this fasting period (at home), patients are not allowed to eat or drink, smoke, or exercise excessively. The test takes 2 hours and is performed at the laboratory’s collection centre. Blood tests are taken at the beginning of the test and at regular intervals after a glucose-containing drink is taken. Sometimes it is possible to take the blood samples from a small plastic tube left in the vein – an intravenous cannula.

Medical Conditions and Symptoms

A Glucose Tolerance Test (GTT) may be ordered by your doctor if they are suspicious of diabetes or impaired glucose tolerance, a milder form of disease which may occur before full-blown diabetes develops. A single fasting or random blood glucose test may show a glucose level high enough to diagnose diabetes, but if there is doubt a glucose tolerance test may be needed. Some women develop impaired glucose tolerance or gestational diabetes during pregnancy only, and a GTT is one way to detect this. Symptoms of diabetes include excessive thirst leading to increased fluid intake (polydipsia), frequent urination or increased urine output (polyuria), weight loss or weight gain, or frequent infections such as thrush (candidiasis) or skin infections.

Test Results Explained

The Glucose Tolerance Test (GTT) result will be forwarded to your doctor after several days. It may show:

  • Normal test
  • Impaired Glucose Tolerance – this is not diabetes, but may progress to diabetes; it usually requires a modification to the diet
  • Diabetes Mellitus – which may require diet control, oral medications, or insulin injections

Related Specialists

Related Procedures

  • Blood Test (venesection)
  • Intravenous Cannulation
  • Pre-operative Anaesthetic assessment

Related Tests

Also Known As

  • Oral Glucose Tolerance Test (OGTT)