Ascertaining hypoglycorrhachia in an acute patient

A study was undertaken in an urgent clinical setting to determine whether the use of a cerebrospinal fluid (CSF) to blood glucose ratio is appropriate for describing the relationships between CSF glucose and blood glucose in patients who had not fasted. Blood glucose levels were obtained before a lumbar puncture in 79 adults who had normal CSF findings. Regression analysis of CSF glucose and blood glucose levels of these patients who had not fasted, as well as data from four published studies of normal blood and CSF glucose levels, indicated that a ratio was not a valid measure of the normal relationship between CSF and blood. Only when the blood glucose level was between 89 and 115 mg/dL was the relationship within the expected “ratio” of 0.60 to 0.70. In hyperglycemic states, the normal relationship may be substantially lower than 0.50. A nomogram is presented which is useful in determining hypoglycorrhachia when the patient is hyperglycemic.