An individual has a plasma glucose level of 110 mg/dL. What would be the approximate glucose concentration in this patient’s cerebrospinal fluid?

An individual has a plasma glucose level of 110 mg/dL. What would be the approximate glucose concentration in this patient’s cerebrospinal fluid?

• A. 33 mg/dL
• B. 55 mg/dL
• C. 66 mg/dL
• D. 110 mg/dL

Answer: (C)

Glucose in cerebrospinal fluid is related to plasma glucose but is lower because it must diffuse across the blood–brain barrier. In a healthy person, CSF glucose is about 60% of the plasma glucose. So with a plasma glucose of 110 mg/dL, the CSF glucose is around 66 mg/dL. This fits the normal CSF glucose range (roughly 40–70 mg/dL) and reflects the diffusion-limited transfer from blood to CSF. The other values would imply a larger deviation from this typical ratio or an abnormal state, whereas 66 mg/dL is the expected approximate concentration.

Glucose in cerebrospinal fluid is related to plasma glucose but is lower because it must diffuse across the blood–brain barrier. In a healthy person, CSF glucose is about 60% of the plasma glucose. So with a plasma glucose of 110 mg/dL, the CSF glucose is around 66 mg/dL. This fits the normal CSF glucose range (roughly 40–70 mg/dL) and reflects the diffusion-limited transfer from blood to CSF. The other values would imply a larger deviation from this typical ratio or an abnormal state, whereas 66 mg/dL is the expected approximate concentration.