Whole blood glucose concentration is lower than plasma by what percent?

• A. 5% lower
• B. 10-15% lower
• C. 20% lower
• D. No difference

Answer: (B)

Glucose is distributed mainly in the plasma water, so plasma glucose reflects the liquid part of blood. Whole blood includes a large fraction of cells (hematocrit), which have less water and actively metabolize glucose. This combination makes the glucose concentration in whole blood fall below the plasma value by about 10–15%. In practical terms, if plasma glucose is 100 mg/dL, whole blood glucose is typically around 85–90 mg/dL. The exact difference depends on the hematocrit: higher hematocrit (more cells) tends to increase the gap, while lower hematocrit narrows it. Clinically, plasma glucose is about 10% higher than whole blood under typical conditions.