In the case of a 21-year-old with back injury, given whole blood glucose 77 mg/dL, serum glucose 88 mg/dL, and CSF glucose 56 mg/dL, which interpretation is most consistent with reference ranges?

• A. The whole blood and serum values are expected but the CSF value is elevated
• B. The whole blood glucose value should be higher than the serum value
• C. All values are consistent with a normal healthy individual
• D. The serum and whole blood values should be identical

Answer: (C)

CSF glucose reflects serum glucose and is normally about 60% of it. With a serum glucose of 88 mg/dL, a CSF glucose around 56 mg/dL is exactly what you’d expect in a healthy individual, since normal CSF glucose typically falls in the roughly 50–70 mg/dL range when serum is in the 80–100 mg/dL range. The whole-blood glucose value being slightly lower than the serum value also fits normal physiology, because glucose is consumed by red cells and whole-blood measurements are typically a bit lower than serum/plasma.

So, these values together align with reference ranges for a healthy person, making them consistent with normal physiology.