Free and total vitamin B12 in cerebrospinal fluid

Free and total vitamin B(12) levels in serum and cerebrospinal fluid (CSF) were bioassayed, since there were no available data on the relationship between free and total vitamin B(12) in CSF or between free vitamin in serum and CSF vitamin B(12). The subjects were 43 neurological patients. Serum levels were normal in 40 of 43 patients. Values for free and total vitamin B(12) in CSF were the same in 42 of 43 patients. Mean CSF vitamin B(12) was 21 mumug./ml. In 17 cases CSF vitamin B(12) equalled free vitamin B(12) level in serum, in 16 cases CSF vitamin B(12) was lower than the free level in serum, and in 10 cases CSF vitamin B(12) was higher than the free vitamin level in serum. There was no apparent diagnostic correlation. The findings suggest that vitamin B(12) is not bound in CSF and that there is some selective control of passage of vitamin B(12) across the blood-CSF barrier.