Diagnosis is still based on measurement of blood glucose, however the 2-hour Oral Glucose Tolerance Test (OGTT) has given way to the simpler Fasting Plasma Glucose (FPG) test as the preferred diagnostic tool. Type 2 diabetes can be diagnosed by the following:
Other names no longer used for IGT include "borderline," "subclinical," "chemical," and "latent" diabetes.
A diagnosis of IGT does not come without risk. People with IGT have a higher occurrence of cardiovascular disease and are at a higher risk of developing type 2 diabetes than those without IGT. Approximately 25% of people with IGT will develop type 2 diabetes. Complications associated with type 2 diabetes that involve the smaller blood vessels (i.e. those affecting the eyes and kidney) however appear to pose a minimal risk for those with IGT.
The prevalence of IGT in the US adult population, based on national surveys in 1976-80 and 1982-84, was estimated to be 11.2%, ranging from 6.4% at age 20-44 years to 22.8% at age 65-74 years. (Data on diabetes prevalence is more recent. During 1991-93, the prevalence of all types of diagnosed diabetes ranged from 5.8% at age 45-64 years to 10.7% at age 65-74 years.)
The risk factors for IGT appear to be similar to those for type 2 diabetes: a family history of diabetes, higher blood glucose levels, obesity, and a sedentary lifestyle.
* The World Health Organization (WHO) defines IGT as fasting plasma glucose less than 140 mg/dl and, after ingestion of 75 g of glucose, a two-hour BG value of 140-199 mg/dl.