In fasting physiology, plasma glucose is higher than whole-blood glucose. Which option best describes this relationship?

In fasting physiology, plasma glucose is higher than whole-blood glucose. Which option best describes this relationship?

• A. Plasma glucose is lower than whole-blood glucose
• B. Plasma glucose is equal to whole-blood glucose
• C. Plasma glucose is higher than whole-blood glucose
• D. Plasma glucose fluctuates independently of whole-blood glucose

Answer: (C)

Plasma glucose is higher than whole-blood glucose because glucose resides in the water of plasma, which is the liquid part of blood, while whole blood includes cells that occupy space and actively metabolize glucose. Red blood cells (and other cells) take up and use glucose, so the concentration of glucose measured in whole blood ends up lower. In fasting samples, this difference is typically about 10–15%, with plasma glucose higher. The other statements don’t fit because they imply the same or opposite relationships or independent fluctuations, which doesn’t reflect how glucose distributes between the plasma water and the cellular components.

Plasma glucose is higher than whole-blood glucose because glucose resides in the water of plasma, which is the liquid part of blood, while whole blood includes cells that occupy space and actively metabolize glucose. Red blood cells (and other cells) take up and use glucose, so the concentration of glucose measured in whole blood ends up lower. In fasting samples, this difference is typically about 10–15%, with plasma glucose higher. The other statements don’t fit because they imply the same or opposite relationships or independent fluctuations, which doesn’t reflect how glucose distributes between the plasma water and the cellular components.