Compared with serum or plasma, whole blood glucose is typically lower by about what percentage?

• A. 5-10%
• B. 10-15%
• C. 15-20%
• D. 20-25%

Answer: (B)

Glucose is mainly in the plasma water portion of blood, and whole blood includes cells that dilute this plasma water and contribute less glucose per volume. Because of the hematocrit effect, the glucose concentration in whole blood ends up lower than in plasma. The typical difference is about 10–15%, so whole-blood glucose is usually around 85–90% of plasma glucose. This is why plasma or serum measurements are generally higher, and why some devices that use whole blood apply a correction factor. The exact percentage can vary with hematocrit, but 10–15% is the standard range.