As part of a routine physical, a fasting plasma glucose is performed on a 45-year-old male and the test result is 105 mg/dL. How should this individual be classified?

• A. Normal for his age
• B. Impaired fasting glucose
• C. Type 1 diabetes mellitus
• D. Type 2 diabetes mellitus

Answer: (B)

Fasting plasma glucose values are interpreted using fixed thresholds, not age. A normal fasting glucose is under 100 mg/dL. Values from 100 to 125 mg/dL are labeled impaired fasting glucose, which is a form of prediabetes. A result of 105 mg/dL falls into this range, so the person is best described as having impaired fasting glucose.

This value does not meet the typical criteria for diabetes, which usually requires a fasting glucose of 126 mg/dL or higher on two separate occasions (or an abnormal result with clear symptoms, or a specific A1C threshold). Also, the classification isn’t based on age, so the idea of “normal for his age” doesn’t apply here because 105 mg/dL is above the normal cutoff.

Finally, distinguishing type 1 from type 2 diabetes cannot be done from fasting glucose alone; additional clinical information and tests would be needed.