Impaired glucose tolerance (IGT)

If an oral glucose test is administered at random to a large population, 1-2% will be found to have unsuspected diabetes.

A much larger group (~5%) fall into an intermediate category referred to as ‘impaired glucose tolerance’ (IGT).

Follow-up shows that some 2-4% of those with IGT go on to develop diabetes annually.

Obesity and lack of physical exercise increases risk of progression to frank diabetes.

The oral glucose tolerance test:

1. After an overnight fast, 75g of glucose is taken in 250-350ml of water.

2. Blood samples are taken in the fasting state and 2 hrs after the glucose has been given.

Note: The concentration of glucose measured in plasma is 10% greater than that of whole blood.

Diabetes:

This is present when the fasting blood glucose (FBG) is > 6.7mmol/L and/or when the 2 hr value is > 10mmol/L. This corresponds to a fasting plasma glucose (FPG) of > 7.8mmol/L and/or > 11.1mmol/L.

IGT:

Present when the FBG is < 6.7mmol/L and when the 2 hr value is 6.7 – 10mmol/L.

IGT can only be diagnosed using the oral glucose tolerance test.