Diagnostic Criteria for Diabetes According to the American Diabetes Association (ADA)
The American Diabetes Association (ADA) recommends using a fasting plasma glucose level of ≥126 mg/dL to make a preliminary diagnosis of diabetes. 1
Diagnostic Criteria for Diabetes
The ADA has established clear criteria for the diagnosis of diabetes mellitus:
- Fasting Plasma Glucose (FPG): ≥126 mg/dL (7.0 mmol/L)
- 2-hour Plasma Glucose during OGTT: ≥200 mg/dL (11.1 mmol/L)
- A1C: ≥6.5% (48 mmol/mol)
- Random Plasma Glucose: ≥200 mg/dL (11.1 mmol/L) with symptoms of hyperglycemia
Confirmation Requirements
- In the absence of unequivocal hyperglycemia with classic symptoms, these criteria should be confirmed by repeat testing 1
- The ADA recommends that the same test be repeated without delay using a new blood sample 1
- If two different tests (such as A1C and FPG) are both above diagnostic thresholds, this also confirms the diagnosis 1
Categories of Increased Risk (Prediabetes)
The ADA also defines categories for increased risk of diabetes:
- Impaired Fasting Glucose (IFG): 100-125 mg/dL (5.6-6.9 mmol/L)
- Impaired Glucose Tolerance (IGT): 2-hour plasma glucose 140-199 mg/dL (7.8-11.0 mmol/L) during OGTT
- A1C: 5.7-6.4% (39-47 mmol/mol)
Important Testing Considerations
- Fasting is defined as no caloric intake for at least 8 hours 1
- Plasma glucose should be measured in an accredited laboratory when used for diagnosis 1
- To minimize glycolysis, blood samples should be collected in tubes containing glycolytic inhibitors or immediately placed in an ice-water slurry 1
Special Populations
- For children and adolescents, the same diagnostic criteria apply 1
- In patients with hemoglobinopathies, anemia, or increased red blood cell turnover, only plasma glucose criteria should be used 1
Common Pitfalls to Avoid
Not confirming the diagnosis: A single abnormal test result is not sufficient for diagnosis unless there are classic symptoms of hyperglycemia with a random plasma glucose ≥200 mg/dL
Using point-of-care testing for diagnosis: The ADA emphasizes that diagnosis must be confirmed by measurement of venous plasma glucose in a clinical chemistry laboratory 1
Misinterpreting stress hyperglycemia: Incidental hyperglycemia during acute illness, especially in children, does not necessarily indicate diabetes 1
Not considering interfering factors for A1C: Hemoglobin variants, anemia, and conditions with increased red blood cell turnover can affect A1C results 1
The ADA's diagnostic threshold of fasting plasma glucose ≥126 mg/dL represents a level at which the prevalence of microvascular complications increases significantly, providing a clinical basis for this cutoff value.