Glucose higher in CSF than plasma

Medical Laboratory Observer, June, 2004 by Andrew M. Schreiner

I am an undergraduate student in a medical laboratory science honors degree program and am currently on assignment in Zimbabwe's largest government hospital. I am in the clinical chemistry lab, and the main analyzer used is the CX5 from Beckman.

A cerebrospinal fluid (CSF) sample in a plain tube and a random blood-sugar specimen in a fluoride (grey) tube from the same patient were run for glucose. The CSF sample was clear, and the plasma after centrifugation appeared nonhemolyzed; there was no sign of bacterial contamination.

Results obtained:

CSF glucose = 4.7 mM/L (85 mg/dL);

Plasma glucose = 4.1mM/L (74 mg/dL)

Is there any possible pathological condition that can result in a higher CSF glucose than that in plasma? What are the possible reasons for this result?

CSF glucose is derived from blood glucose. CSF glucose concentrations are typically 60% of plasma levels; normal concentrations ranging from 50 mg/dL to 80 mg/dL. (1) Although there are many causes of low CSF glucose, hyperglycemia is the only known cause of hyperglycorrhachia (elevated CSF glucose). CSF glucose levels generally do not rise above 300 mg/dL (16.7 mmol/L), even in cases of extreme hyperglycemia. (2)

Equilibration of glucose between plasma and CSF takes approximately two hours; therefore, CSF glucose reflects plasma glucose from a few hours earlier. (3) A CSF glucose value greater than that seen in plasma may occur if the CSF has been collected immediately following exposure to a hypoglycemic agent, such as insulin. In the case described, CSF glucose of 4.7 mmol/L (85 mg/dL) and plasma glucose of 4.1 mmol/L (74 mg/dL) may represent values obtained soon after patient exposure to an insulin. The rapid fall in plasma glucose due to a hypoglycemic agent, with insufficient time being allowed for the CSF glucose to equilibrate, can explain these findings. (4)

References

1. Henry JB, ed. Clinical Diagnosis and Management by Laboratory Methods. 20th ed, Philadelphia, PA. WB Saunders Company; 2001.

2. Dougherty JM, Roth RM. Cerebral spinal fluid Emerg Med Clin. 1986;4:281-297.

3. Seehusen DA, Reeves MM, Fomin DA. Cerebrospinal fluid analysis. Am Fam Physician, 2003;68:1103-1108.

4. Arieff AI, Carroll HJ. Cerebral edema and depression of sensorium in nonketotic hyperosmolar coma. Diabetes, 1974;23:525-531.

--Andrew M. Schreiner, MD

Department of Pathology

Oregon Health and Science University

Portland, OR