Fasting plasma glucose (FPG), two-hour plasma glucose during a 75 g oral glucose tolerance test (OGTT), or glycated hemoglobin (A1C) may be used for diagnostic testing.
Symptomatic hyperglycemia — The diagnosis of diabetes mellitus is easily established when a patient presents with classic symptoms of hyperglycemia (thirst, polyuria, weight loss, blurry vision) and has a random blood glucose value of 200 mg/dL (11.1 mmol/L) or higher. Most patients with type 1 diabetes are symptomatic and have plasma glucose concentrations well above ≥200 mg/dL. Some patients with type 2 diabetes also present with symptomatic hyperglycemia and blood glucose ≥200 mg/dL.
| American Diabetes Association criteria for the diagnosis of diabetes
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| 1. | A1C ≥6.5%. The test should be performed in a laboratory using a method that is NGSP certified and standardized to the DCCT assay.
OR
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| 2. | FPG ≥126 mg/dL (7 mmol/L). Fasting is defined as no caloric intake for at least 8 hours.
OR
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| 3. | 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an OGTT. The test should be performed as described by the World Health Organization, using a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water.
OR
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| 4. | In a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose ≥200 mg/dL (11.1 mmol/L). |
Asymptomatic hyperglycemia — The diagnosis of diabetes in an asymptomatic individual (generally type 2 diabetes) can be established with any of the following criteria:-
- FPG values ≥126 mg/dL (7.0 mmol/L).
- Two-hour plasma glucose values of ≥200 mg/dL (11.1 mmol/L) during a 75 g OGTT.
- A1C values ≥6.5 percent (48 mmol/mol).
The ADA criteria to diagnose prediabetes are as follows: –
- Impaired fasting glucose (IFG)– FPG between 100 and 125 mg/dL (5.6 to 6.9 mmol/L). The World Health Organization (WHO) defines IFG as an FPG of 110 to 125 mg/dL (6.1 to 6.9 mmol/L)
- Impaired glucose tolerance (IGT)– Two-hour plasma glucose value during a 75 g OGTT between 140 and 199 mg/dL (7.8 to 11.0 mmol/L). The WHO defines IGT as a two-hour, post-OGTT glucose ≥140 mg/dL (7.8 mmol/L) but <200 mg/dL (11.1 mmol/L) and a FPG <126 (7.0 mmol/L)
- A1C– Persons with A1C 5.7 to <6.5 percent (39 to 48 mmol/mol; 6.0 to <6.5 percent [42 to 48 mmol/mol].
| Categories of increased risk for diabetes (prediabetes) | |
| 1. | FPG 100 to 125 mg/dL (5.6 to 6.9 mmol/L) – IFG |
| 2. | 2-hour post-load glucose on the 75 g OGTT 140 to 199 mg/dL (7.8 to 11.0 mmol/L) – I |
| 3. | A1C 5.7 to 6.4% (39 to 46 mmol/mol) |
