Impaired Glucose Tolerance Diagnosis and Management

Definition and Diagnostic Criteria

The American Diabetes Association defines impaired glucose tolerance (IGT) as 2-hour post-load plasma glucose levels between 140-199 mg/dL (7.8-11.0 mmol/L) during an oral glucose tolerance test, with fasting glucose below the diabetic threshold 1, 2
IGT is diagnosed when 2-hour plasma glucose levels during a 75g oral glucose tolerance test (OGTT) are between 140-199 mg/dL (7.8-11.0 mmol/L), while fasting glucose remains below the diabetic threshold 3, 4
IGT often coexists with impaired fasting glucose (IFG), which is defined as fasting plasma glucose between 100-125 mg/dL (5.6-6.9 mmol/L) after at least 8 hours of fasting, according to the American College of Physicians 1, 2

The European Association for the Study of Diabetes notes that IGT is part of the broader metabolic syndrome, frequently coexisting with other cardiovascular risk factors such as obesity, hypertension, and dyslipidemia 1
In the Diabetes Prevention Program (DPP), individuals with IGT and elevated BMI had a crude incidence of diabetes of 11.0 cases per 100 person-years, with a cumulative 3-year incidence of 28.9%, as reported by the American Diabetes Association 5

Risk factors for IGT include overweight and obesity, particularly abdominal/visceral obesity, as stated by the American Heart Association 1
Physical inactivity is a risk factor for IGT, according to the American College of Sports Medicine 4
History of gestational diabetes is a risk factor for IGT, as noted by the American College of Obstetricians and Gynecologists 5

The U.S. Preventive Services Task Force recommends screening for abnormal blood glucose in adults aged 40-70 years who are overweight or obese, as stated in the guidelines from the American College of Preventive Medicine 6, 2
Screening can be done using HbA1c, fasting plasma glucose, or an oral glucose tolerance test, according to the American Academy of Family Physicians 4

Lifestyle modifications, including dietary modifications focusing on reduced caloric intake, are the cornerstone of management for IGT, as recommended by the American Heart Association 4
Intensive behavioral interventions that combine counseling on healthful diet and physical activity have shown benefit in reducing progression to diabetes, according to the American College of Lifestyle Medicine 6

Regression from IGT to normal glucose tolerance has been associated with lower risk of cardiovascular and microvascular disease over the long term, as reported by the American Diabetes Association 5

The oral glucose tolerance test is more sensitive but less convenient than fasting glucose for identifying prediabetes, as noted by the American College of Physicians 2
Not all individuals with IGT will progress to diabetes; approximately one-third may revert to normal glucose tolerance, according to the American Heart Association 7
IGT should not be viewed simply as a pre-disease state but as a condition that independently increases cardiovascular risk, as stated by the European Society of Cardiology 3