What is the role of oral glucose tolerance testing (GTT) in the diagnosis of diabetes?

Updated: May 10, 2021
  • Author: Jiun-Lih Jerry Lin, MBBS, MS(Orth); Chief Editor: Eric B Staros, MD  more...
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Oral GTT is currently the criterion standard for the diagnosis of diabetes in Australia. It is indicated when the results of fasting or random blood glucose are equivocal towards the diagnosis of type 2 diabetes mellitus, such as the following:

  • Fasting blood glucose: 5.5–6.9 mmol/L

  • Random blood glucose: 5.5–11 mmol/L

Oral GTT is unnecessary if fasting or random blood glucose levels are clearly in the nondiabetic or diabetic range (refer to Reference Range section).

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