Diagnostic Criteria for Non-Pregnant Individuals

Diagnostic Thresholds

The American Diabetes Association recommends that a normal 2-hour plasma glucose during a 75-gram OGTT is less than 140 mg/dL (7.8 mmol/L) for non-pregnant adults 1
The American Diabetes Association establishes clear cutoffs that define the boundaries between normal, prediabetes, and diabetes for the OGTT, with a 2-hour plasma glucose of 140-199 mg/dL (7.8-11.0 mmol/L) indicating prediabetes 1, 2
The American Diabetes Association defines diabetes as a 2-hour plasma glucose of ≥200 mg/dL (≥11.1 mmol/L) during a 75-gram OGTT 1, 2, 3

Patients must consume at least 150 grams of carbohydrates daily for the 3 days prior to the OGTT to ensure accurate results, as recommended by the American Diabetes Association 1, 2
The World Health Organization methodology requires an 8-hour fast before administration of 75 grams of anhydrous glucose dissolved in water 1, 2, 3

The American Diabetes Association notes that glycolysis is a critical concern that can falsely lower glucose concentrations if samples are not processed promptly or stored properly prior to analysis 1, 2
Recent physical activity, acute illness, acute stress, and high diurnal variation in glucose levels can acutely affect glucose concentrations and should be considered when interpreting results, according to the American Diabetes Association 1, 2, 3

The American Diabetes Association recommends that in the absence of unequivocal hyperglycemia, diagnosis of diabetes requires two abnormal test results obtained either at the same time or at two different time points 1, 2, 3

The American Diabetes Association notes that risk is continuous across the entire glucose spectrum, extending below the lower limit of the prediabetes range and becoming disproportionately greater at the higher end 1, 2

The American Diabetes Association recommends fasting plasma glucose (normal: <100 mg/dL) as an alternative diagnostic test for diabetes or prediabetes 1
The American Diabetes Association recommends A1C (normal: <5.7%) as an alternative diagnostic test for diabetes or prediabetes 1

The American Diabetes Association recommends HbA1c as the preferred initial test for diagnosing diabetes in non-pregnant adults, due to its convenience, preanalytical stability, and lack of fasting requirement 4, 5
HbA1c ≥6.5% indicates diabetes, while OGTT with 2-hour plasma glucose ≥200 mg/dL after a 75-gram glucose load also indicates diabetes 4, 5

HbA1c offers several practical advantages over OGTT, including no fasting required, greater preanalytical stability, and lower day-to-day variability 4, 5
HbA1c reflects average glycemia over 2-3 months and has well-standardized assays when NGSP-certified 4, 5

OGTT is preferred over HbA1c in situations such as hemoglobin variants, altered erythrocyte turnover, pregnancy, HIV infection, hemodialysis or renal failure, and cirrhosis 4, 5

HbA1c has limitations, including lower sensitivity and potential for systematic bias, and point-of-care testing should only be done with FDA-approved devices at CLIA-certified laboratories 4, 5
OGTT has limitations, including high within-person variability, requirement for patient preparation, and potential for acute factors to alter results 4, 5

Confirmation is required when using either test, and a repeat test or a different test should be performed to confirm the diagnosis 4, 5
In cases of discordant results, the test that was above the diagnostic threshold should be repeated 4, 5

Point-of-care HbA1c devices should not be used unless they are FDA-approved for diagnosis and used in properly certified laboratories 4, 5
HbA1c should not be relied upon solely when the clinical picture doesn't match, and plasma glucose testing should be used when results are equivocal or discordant 4, 5