From the Guidelines
Diabetes mellitus is diagnosed when a patient meets one or more of the following criteria: a fasting plasma glucose level of 126 mg/dL (7.0 mmol/L) or higher, a 2-hour plasma glucose level of 200 mg/dL (11.1 mmol/L) or higher during an oral glucose tolerance test, a random plasma glucose level of 200 mg/dL or higher in a patient with classic symptoms of hyperglycemia, or a hemoglobin A1C level of 6.5% or higher, as recommended by the most recent guidelines 1.
Diagnostic Criteria
The diagnostic criteria for diabetes mellitus include:
- A1C ≥ 6.5%, with the test performed in a laboratory using a method that is NGSP certified and standardized to the DCCT assay
- FPG ≥ 126 mg/dL (7.0 mmol/L), with fasting defined as no caloric intake for at least 8 hours
- 2-h PG ≥ 200 mg/dL (11.1 mmol/L) during an OGTT, performed as described by the WHO
- Random plasma glucose ≥ 200 mg/dL (11.1 mmol/L) in a patient with classic symptoms of hyperglycemia or hyperglycemic crisis
Confirmation of Diagnosis
In the absence of unequivocal hyperglycemia, results should be confirmed by repeat testing, as stated in the guidelines 1. If two different tests are available in an individual and the results are discordant, the test whose result is above the diagnostic cut point should be repeated, and the diagnosis is made on the basis of the confirmed test.
Considerations for Certain Conditions
For patients with certain hemoglobinopathies or anemias, A1C levels may be problematic to interpret, and only blood glucose criteria should be used to diagnose diabetes, as noted in the guidelines 1. In conditions associated with increased red cell turnover, such as pregnancy, recent blood loss or transfusion, erythropoietin therapy, or hemolysis, only blood glucose criteria should be used to diagnose diabetes.
Importance of Standardized Laboratory Methods
When testing for diabetes, it's essential to use a standardized laboratory method rather than point-of-care devices for initial diagnosis, as emphasized in the guidelines 1, to ensure accurate results and proper diagnosis.
From the Research
Diagnostic Criteria for Diabetes Mellitus (DM)
The diagnostic criteria for Diabetes Mellitus (DM) are established through various methods, including:
- History and physical examination 2
- Measurements of serum or plasma glucose concentrations under specific conditions 2
- Detection of abnormally high levels of glycemia 3
- Fasting plasma glucose (FPG) ≥ 126 mg/dL 4, 5, 6
- 2-hour plasma glucose (2hPG) ≥ 200 mg/dL 4, 6
- Hemoglobin A1c (HbA1c) ≥ 6.5% 4, 5, 6
- Random plasma glucose level of 200 mg per dL or greater 6
Diagnostic Tests
The following diagnostic tests are used to diagnose DM:
- Fasting plasma glucose test 4, 5, 6
- 2-hour plasma glucose test 4, 6
- Hemoglobin A1c test 4, 5, 6
- 75-g two-hour oral glucose tolerance test 6
- Random plasma glucose test 6
Screening and Diagnosis
Screening for DM is recommended for:
- Adults 40 to 70 years of age who are overweight or obese 6
- Individuals at higher risk for DM, such as those with a family history or major risk factors 6
- Patients 45 years and older, or patients younger than 45 years with major risk factors 6 The diagnosis of DM can be made with a single test result, but results should be confirmed with repeat testing on a subsequent day, unless a single random plasma glucose level of 200 mg per dL or greater is accompanied by typical signs and symptoms of hyperglycemia 6