Which of the following is a diagnostic criterion for diabetes?

• A. HbA1c >= 7.0%
• B. Fasting plasma glucose >= 126 mg/dL
• C. Random plasma glucose >= 200 mg/dL
• D. HbA1c >= 6.5%

Answer: (D)

Diabetes is defined by specific laboratory thresholds rather than by symptoms alone, and HbA1c provides a reliable reflection of average glucose over the past two to three months. An HbA1c level of 6.5% or higher meets the diagnostic criterion for diabetes, making it a clear and widely used threshold because it does not require fasting and is reproducible across labs. The 7.0% figure is more often used as a general treatment target to guide therapy, not as the diagnostic cutoff. Fasting plasma glucose of 126 mg/dL or higher is also diagnostic, but it requires the patient to fast and is typically confirmed on a separate day. A random plasma glucose of 200 mg/dL or higher with classic hyperglycemic symptoms can diagnose diabetes as well, though timing and symptom presence matter. In this context, the HbA1c threshold of 6.5% stands out as a definitive diagnostic criterion.