From the Guidelines
A fasting glucose level of ≥ 126 mg per dL (7.0 mmol per L) is diagnostic for Type 2 Diabetes Mellitus (TIIDM). This threshold is based on the criteria outlined in the American family physician study 1, which represents the point at which the risk of microvascular complications increases significantly. Fasting means no caloric intake for at least 8 hours prior to the blood test. For proper diagnosis, the elevated reading should be confirmed with a repeat test on a different day unless there are clear symptoms of hyperglycemia or a random glucose level over 200 mg per dL (11.1 mmol per L).
Diagnostic Criteria
Other diagnostic criteria for TIIDM include:
- A 2-hour plasma glucose level of ≥ 200 mg per dL (11.1 mmol per L) during an oral glucose tolerance test (OGTT) 1
- A hemoglobin A1C of ≥ 6.5% 1
- A random glucose test of ≥ 200 mg per dL with symptoms 1 It's essential to note that these criteria should be confirmed by repeat testing on a different day in the absence of unequivocal hyperglycemia 1. The pathophysiology behind these elevated glucose levels involves insulin resistance in peripheral tissues and relative insulin deficiency, where the pancreas cannot produce enough insulin to overcome this resistance, resulting in chronic hyperglycemia.
Key Considerations
Key considerations in diagnosing TIIDM include:
- The ease of testing with A1C measurement, which does not require fasting 1
- The limitations of A1C testing, including low sensitivity, possible racial disparities, and interference by anemia and some medications 1
- The importance of confirming the diagnosis with repeat testing on a different day unless there are clear symptoms of hyperglycemia or a random glucose level over 200 mg per dL (11.1 mmol per L) 1
From the Research
Diagnostic Criteria for Type 2 Diabetes Mellitus (TIIDM)
The diagnostic criteria for TIIDM include a fasting plasma glucose level of 126 mg/dL or greater 2, 3, 4.
- A fasting plasma glucose level of 126 mg/dL or greater is considered diagnostic for TIIDM 2, 3, 4
- The American Diabetes Association recommends screening for type 2 diabetes annually in patients 45 years and older, or in patients younger than 45 years with major risk factors 2
- The diagnosis can also be made with an A1C level of 6.5% or greater, a random plasma glucose level of 200 mg/dL or greater, or a 75-g two-hour oral glucose tolerance test with a plasma glucose level of 200 mg/dL or greater 2, 3, 4
Fasting Plasma Glucose Levels
The fasting plasma glucose level is a key diagnostic criterion for TIIDM.
- A level of 126 mg/dL or greater is considered diagnostic for TIIDM 2, 3, 4
- A level between 100 and 125 mg/dL is considered impaired fasting glucose, which is a precursor to TIIDM 3
- The threshold of fasting plasma glucose defining impaired fasting glucose is still debated 3
Comparison of Diagnostic Criteria
Different studies have compared the diagnostic criteria for TIIDM.
- One study found that a fasting plasma glucose level of 126 mg/dL or greater was a reliable diagnostic criterion for TIIDM 2
- Another study found that the threshold of fasting plasma glucose defining impaired fasting glucose was still debated 3
- A third study found that the American Diabetes Association's diagnostic criteria for TIIDM were effective in identifying patients with the disease 4