What is the workup for diabetes (DIAB)

From the Guidelines

The workup for diabetes should start with a fasting plasma glucose test (FPG) or a hemoglobin A1C test, with levels ≥126 mg/dL or ≥6.5% respectively indicating diabetes, as recommended by the most recent guidelines 1. The diagnosis of diabetes requires two abnormal test results from the same sample or in two separate test samples, with the second test performed without delay if using two separate test samples.

• Fasting plasma glucose (FPG) test with levels ≥126 mg/dL indicating diabetes
• Hemoglobin A1C test with values ≥6.5% confirming the diagnosis
• Oral glucose tolerance test (OGTT) with a 2-hour plasma glucose ≥200 mg/dL after a 75g glucose load indicating diabetes
• Random plasma glucose ≥200 mg/dL with classic symptoms (polyuria, polydipsia, unexplained weight loss) is also diagnostic Once diabetes is confirmed, additional tests should include:
• Comprehensive metabolic panel to assess kidney function
• Lipid profile to evaluate cardiovascular risk
• Urinalysis to check for albuminuria
• Thyroid function tests since thyroid disorders often coexist with diabetes Baseline eye and foot examinations are essential to detect early complications, as diabetes affects multiple organ systems, and early detection of complications allows for timely intervention to prevent disease progression, as noted in the guidelines 1. It is critical to follow the patient closely and repeat the test in 3–6 months if patients have test results near the margins of the diagnostic threshold, considering the potential for preanalytic variability in glucose samples 1. The diagnostic criteria reflect the blood glucose thresholds at which microvascular complications begin to develop, making accurate diagnosis vital for appropriate management, as emphasized in the guidelines 1.

From the Research

Diagnostic Criteria for Diabetes

The diagnosis of diabetes can be made using several criteria, including:

• Hemoglobin A1c (HbA1c) level greater than or equal to 6.5% 2, 3
• Fasting plasma glucose level greater than or equal to 126 mg/dL 3, 4
• 2-hour postglucose-load plasma glucose level greater than or equal to 200 mg/dL 3
• Casual plasma glucose level greater than or equal to 200 mg/dL 3

Diagnostic Workup

The diagnostic workup for diabetes typically involves:

• Measurement of HbA1c level 2, 3
• Measurement of fasting plasma glucose level 3, 4
• Oral glucose tolerance test (OGTT) to measure 2-hour postglucose-load plasma glucose level 3
• Clinical evaluation to assess for symptoms of diabetes, such as polydipsia, polyuria, and weight loss 3

Limitations of HbA1c Testing

HbA1c testing has several limitations, including:

• May not accurately reflect glucose levels in patients with certain medical conditions, such as hemoglobinopathies or chronic kidney disease 2
• May not detect all cases of diabetes, particularly in patients with impaired glucose tolerance 5, 4
• Should be used in combination with plasma glucose measurements to confirm the diagnosis of diabetes 2, 4

Combination of Diagnostic Tests

Using a combination of diagnostic tests, such as HbA1c and fasting plasma glucose, may improve the accuracy of diabetes diagnosis and identify more people at risk of developing diabetes 6, 4.