Glucose, Cerebrospinal Fluid

Elevation implies hyperglycemia two to four hours earlier. Significantly decreased cerebrospinal fluid glucose levels are <40 mg/dL in fasting patient with normal plasma glucose. The frequency of low CSF glucose in bacterial meningitis varies somewhat between series; a major textbook of pediatrics points out that acute viral meningitis is often differentiated from acute bacterial meningitis, because the latter is characterized by a CSF glucose <30 mg/dL, a CSF glucose:blood glucose ratio <0.2−0.3 as well as a protein >200 mg/dL, a CSF PMN count >1000/mm³ and an 80% to 90% likelihood of positive Gram stain, in an illness often occurring during the winter in a child younger than two years of age.¹ The magnitude of the seasonal curves for viral versus bacterial meningitis (the former more frequent in the summer) is greater than most clinicians appreciate.² In 134 Gram stain positive cases, CSF glucose was 14.4/30.6/50.4 mg/dL, 25th/percentile median/75th percentile.² The gold standard for the diagnosis of bacterial meningitis is the culture.^3,4 Decreased CSF glucose is characteristically but not invariably found in tuberculous, fungal and amebic meningitis (Naegleria) as well as in bacterial meningitis. Glucose is usually normal in viral meningitis, but in herpes or mumps meningoencephalitis, lymphocytic choriomeningitis, and enteroviruses, glucose may be low. Sarcoidosis and neurosyphilis are reported causes of low CSF glucose. Other very uncommon causes of low CSF glucose include meningeal cysticercosis, trichinosis, and with the chemical meningitis which accompanies intrathecal therapy. Low CSF glucose may also occur in subarachnoid hemorrhage and neoplasia (eg, medulloblastoma). Low CSF glucose may be found in CNS leukemia. Decrease has led to the diagnosis of insulinoma presenting with CNS symptoms. Rheumatoid meningitis and lupus myelopathy may cause low CSF glucose.⁵ CSF glucose levels ≤20 mg/dL are highly correlated with bacterial meningitis.⁶ Lactic acid may be useful in the diagnosis of bacterial meningitis, but values overlap those found with viral meningitis (aseptic meningitis).⁵