From the Guidelines
Type 2 diabetes mellitus is diagnosed when a patient meets one or more of the following criteria: fasting plasma glucose ≥126 mg/dL (7.0 mmol/L) after at least 8 hours of fasting; 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test using 75g of glucose; hemoglobin A1C ≥6.5% (48 mmol/mol); or random plasma glucose ≥200 mg/dL (11.1 mmol/L) in a patient with classic symptoms of hyperglycemia such as polyuria, polydipsia, and unexplained weight loss, as stated in the most recent guidelines 1.
Diagnosis Criteria
The diagnosis of type 2 diabetes mellitus is based on the following criteria:
- Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L) after at least 8 hours of fasting
- 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test using 75g of glucose
- Hemoglobin A1C ≥6.5% (48 mmol/mol)
- Random plasma glucose ≥200 mg/dL (11.1 mmol/L) in a patient with classic symptoms of hyperglycemia Unless there is a clear clinical picture with significantly elevated glucose levels, a second test should be performed to confirm the diagnosis, as recommended by the latest standards of care in diabetes-2025 1.
Screening Recommendations
Testing should be considered in adults who are overweight or obese (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans) with one or more risk factors, including:
- First-degree relative with diabetes
- High-risk race/ethnicity
- History of cardiovascular disease
- Hypertension
- HDL cholesterol <35 mg/dL
- Physical inactivity
- Conditions associated with insulin resistance All adults should be screened starting at age 45 regardless of risk factors, with repeat testing every 3 years if results are normal, as suggested by the guidelines 1.
Importance of Early Diagnosis
Early diagnosis is crucial as it allows for prompt intervention to prevent complications such as retinopathy, nephropathy, neuropathy, and cardiovascular disease. The latest study 1 emphasizes the importance of early detection and treatment of type 2 diabetes to improve patient outcomes and reduce the risk of long-term complications.
From the Research
Diagnosis of Type 2 Diabetes Mellitus
- The diagnosis of type 2 diabetes mellitus can be made using various tests, including fasting plasma glucose, hemoglobin A1c, and the oral glucose tolerance test 2.
- 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 3.
- The diagnosis can be made with a fasting plasma glucose level of 126 mg per dL or greater; an A1C level of 6.5% or greater; a random plasma glucose level of 200 mg per dL or greater; or a 75-g two-hour oral glucose tolerance test with a plasma glucose level of 200 mg per dL or greater 3.
Diagnostic Tests
- Hemoglobin A1c (HbA1c) is a useful test for the diagnosis of diabetes, with a recommended cut-off point of 6.5% 4.
- However, HbA1c testing has the potential for systematic error, and factors such as patient factors and laboratory variability can impact test results 4.
- Fasting plasma glucose and oral glucose tolerance tests are also recommended for the diagnosis of diabetes, particularly in cases where HbA1c testing is not possible or is inconclusive 4.
- A systematic review and meta-analysis found that the optimal cut-off for diagnosing diabetes with HbA1c was estimated as 6.03% with a pooled sensitivity of 73.9% and specificity of 87.2% 5.
Diagnostic Thresholds
- The optimal cut-off for fasting plasma glucose was estimated as 104 mg/dL with a sensitivity of 82.3% and specificity of 89.4% 5.
- A meta-analysis found that a 1-hour plasma glucose level of 11.6 mmol/L during the oral glucose tolerance test had a sensitivity of 0.92 and specificity of 0.91 for detecting type 2 diabetes 6.
- The use of a diabetes-specific risk calculator to identify high-risk individuals may help decrease the proportion of false-positive cases 6.