What are the diagnostic criteria for pre-diabetes (impaired glucose tolerance)?

From the Guidelines

Prediabetes is diagnosed when blood glucose levels are higher than normal but not high enough to be classified as type 2 diabetes, with diagnosis criteria including a fasting blood glucose level between 100-125 mg/dL (5.6-6.9 mmol/L), a 2-hour plasma glucose level of 140-199 mg/dL (7.8-11.0 mmol/L) during an oral glucose tolerance test, or a hemoglobin A1C (HbA1C) level between 5.7-6.4%. These tests measure how effectively your body processes glucose, with fasting blood glucose evaluating your blood sugar after not eating for at least 8 hours, the oral glucose tolerance test assessing how your body responds to sugar consumption, and HbA1C reflecting your average blood sugar over the past 2-3 months 1.

Key Points to Consider

• The diagnosis criteria for prediabetes are based on the results of three tests: fasting plasma glucose (FPG), 2-hour plasma glucose during an oral glucose tolerance test (OGTT), and hemoglobin A1C (HbA1C) 1.
• The FPG test measures blood glucose levels after an overnight fast, the OGTT measures blood glucose levels after consuming a sugary drink, and the HbA1C test measures average blood glucose levels over the past 2-3 months 1.
• Lifestyle modifications, including weight loss, regular physical activity, and dietary changes, can significantly reduce the risk of progression to type 2 diabetes by improving insulin sensitivity and glucose metabolism 1.
• Regular monitoring with repeat testing every 1-2 years is important to track progression or improvement, with at least annual monitoring recommended for those with prediabetes 1.

Important Considerations

• The American Diabetes Association recommends screening for prediabetes and type 2 diabetes risk through an informal assessment of risk factors or with an assessment tool, such as the American Diabetes Association risk test 1.
• Those determined to be at high risk for type 2 diabetes, including people with A1C 5.7–6.4% (39–47 mmol/mol), impaired glucose tolerance, or impaired fasting glucose, are ideal candidates for diabetes prevention efforts 1.
• Using A1C to screen for prediabetes may be problematic in the presence of certain hemoglobinopathies or conditions that affect red blood cell turnover 1.

From the Research

Pre-Diabetes Diagnosis Criteria

The diagnosis of pre-diabetes is based on several criteria, including:

• Fasting glucose level of 100 to 125 mg/dL 2, 3
• Glucose level of 140 to 199 mg/dL measured 2 hours after a 75-g oral glucose load 2, 3
• Glycated hemoglobin level (HbA1C) of 5.7% to 6.4% or 6.0% to 6.4% 2, 3

Comparison of Diagnostic Criteria

Studies have compared the effectiveness of these criteria in diagnosing pre-diabetes and diabetes, including:

• A study that found HbA1c ≥ 6.5% detects less than 50% of diabetic patients defined by FPG and less than 30% of diabetic patients defined by 2hPG 4
• A study that found prediabetes defined by HbA1c and/or FPG criteria is associated with markers of diabetic macro- and micro-vascular disease, but not after statistical adjustment 5

Association with Other Conditions

Pre-diabetes has been associated with an increased risk of:

• Diabetes 2, 3
• Cardiovascular events 2, 5
• Mortality 2
• Hypertension 6

Diagnostic Thresholds

The thresholds for diagnosing pre-diabetes and diabetes are still debated, including:

• The threshold of fasting plasma glucose defining Impaired Fasting Glucose 3
• The adequacy of HbA1c as a correct diagnostic tool for pre-diabetes 3