Vitamin B12 in CSF: reduced CSF/serum B12 ratio in demented men.

Vitamin B12 concentrations were determined in serum and cerebrospinal fluid (CSF) of 32 controls and 102 patients with dementia. The dementias were classified as Alzheimer's disease (AD), senile dementia of Alzheimer type (SDAT) and multi-infarct dementia (MID). A substantial number of patients (n = 42) could not be assigned to any of these diagnostic groups, as their dementias were of non-AD/SDAT and non-MID types. They were instead assigned to a group called non ultra descriptum (NUD). CSF B12 correlated significantly with serum B12. There were no statistically significant differences in serum B12 levels between the groups. Although with considerable overlap, CSF B12 concentrations and CSF/serum B12 ratios were significantly lower in the NUD group than in the control group. The NUD group had significantly lower CSF/serum B12 ratios than the group of patients with AD/SDAT. There was significant male predominance in the group of demented patients that had low CSF/serum B12 ratios outside the bivariate reference region. CSF and serum B12 levels appear insufficient as measures of the true brain vitamin B12 status. It may be a more dynamic approach to use the CSF/serum B12 ratio as an indication of transport function across the blood brain barrier, and possibly also across the CSF brain cell barrier.