Which diagnostic criterion is used to classify diabetes mellitus via HbA1c?

• A. HbA1c ≥ 6.5%
• B. Fasting plasma glucose ≥ 126 mg/dL
• C. 2-hour plasma glucose ≥ 200 mg/dL after an OGTT
• D. Random plasma glucose ≥ 200 mg/dL with symptoms

Answer: (A)

HbA1c measures the percentage of glycated hemoglobin, reflecting average blood glucose over the past about 2–3 months because red blood cells live that long. Because it doesn’t require fasting and is relatively stable from day to day, it’s a convenient way to diagnose diabetes. The diagnostic threshold used is an HbA1c of 6.5% or higher; values in the 5.7–6.4% range indicate prediabetes, while lower values are considered normal. Be aware that certain conditions affecting red blood cell turnover or hemoglobin variants can distort HbA1c accuracy, in which case fasting plasma glucose, the oral glucose tolerance test, or a random glucose with symptoms may be used for classification.