What is the purpose of glucose tolerance testing (GTT)?

Updated: May 10, 2021
  • Author: Jiun-Lih Jerry Lin, MBBS, MS(Orth); Chief Editor: Eric B Staros, MD  more...
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Answer

Answer

Glucose tolerance testing (GTT) is used to evaluate the ability to regulate glucose metabolism and is indicated when random/fasting blood glucose testing alone is insufficient in establishing or ruling out the diagnosis of diabetes mellitus. [1]

Table 1. Fasting Blood Glucose [2, 3] (Open Table in a new window)

 

Australia/United Kingdom

North America

Nondiabetic

< 5.5 mmol/L

< 110 mg/dL

Impaired glucose tolerance

5.5-6.9 mmol/L

110-126 mg/dL

Diabetic

>7 mmol/L

>126 mg/dL

Table 2. Random Blood Glucose [2, 3] (Open Table in a new window)

 

Australia/United Kingdom

North America

Nondiabetic

< 5.5 mmol/L

< 110 mg/dL

Impaired glucose tolerance

5.5-11 mmol/L

110-180 mg/dL

Diabetic

>11 mmol/L

>180 mg/dL

The reference range of serum or plasma glucose is less than 140 mg/dL at 2 hours after a 75-g glucose load.


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