Each 1% increase in HbA1c corresponds to an approximate rise in plasma glucose of how many mg/dL?

• A. 35 mg/dL
• B. 10 mg/dL
• C. 50 mg/dL
• D. 20 mg/dL

Answer: (A)

HbA1c reflects the average glucose over the past 2–3 months because glucose binds to hemoglobin in red blood cells during their lifespan. As average glucose rises, HbA1c rises in a roughly linear fashion, so small changes in HbA1c correspond to meaningful changes in mean glucose. A commonly used teaching rule of thumb is that for each 1% increase in HbA1c, the estimated average plasma glucose goes up by about 35 mg/dL. So if HbA1c increases by 1 percentage point, you’d expect the average glucose to be higher by roughly 35 mg/dL. Note that exact conversions can vary, with some sources using around 29 mg/dL per 1% HbA1c, but the 35 mg/dL figure is a widely used rounding in many exam contexts.