Managing Diabetes

Impaired Glucose Tolerance

What is Impaired Glucose Tolerance (IGT)?

IGT is a pre-diabetic state which is associated with insulin resistance and increased cardiovascular risk. IGT may precede type 2 diabetes by many years.

How is IGT diagnosed?

This requires and Oral Glucose Tolerance test. (OGTT). Fasting plasma glucose is less than 6.0 mmol/l. Two hours after a 75 g oral glucose load, the plasma glucose will be greater than 7.8 mmol/l though less than 11.1 mmol/l.

Why should the 2 hour plasma glucose be less than 11.1 mmol/l ?

This is the cut-off for diagnosing diabetes. 11.1 mmol/l is equivalent to a concentration of 200 mg/dl.

Why is there a greater risk of coronary heart disease?

There is evidence that IGT is often accompanied by damage to the walls of blood vessels, which is caused by inflammatory changes. These changes predispose to the development of atherosclerosis and heightened cardiovascular risk.

What is the evidence in favour of the above?

An American study NHANES II, examined the resulted of an oral glucose tolerance test in over 3000 adults who were followed up over several years.  The risk of death from cardiovascular disease increased in parallel with the 2 hour plasma glucose concentration, in those who did not have diabetes.

What is Impaired fasting Glucose?

Impaired fasting Glucose (IFG) is defined as a fasting plasma glucose greater than 6.0 mmol/l though less than 7.0 mmol/l which is the cut-off for diagnosing diabetes.


Dr Nishan Wijenaike, Consultant Physician
West Suffolk Diabetes Service
August 2003