In most clinical facilities,
the low end of the normal range of vitamin B12
levels is around 200 pg/ml. In order to avoid the
development of neuropsychiatric symptoms, the
vitamin B12 levels should actually be much higher.
Domisse has recommended that every person’s
vitamin B12 levels should be at least 600 pg/ml, and
should actually be over 1000 pg/ml to maximize
mental functioning (4).
An increased mean corpuscular volume (MCV) cannot be used as a
substitute for an evaluation of a patient’s vitamin
B12 level. While it is true that a patient with an
increased MCV will often have decreased vitamin
B12 levels, this has been found to be incorrect 28%
of the time (5).
Another problem associated with vitamin B12
deficiency is that many clinicians are unaware of
how commonly this clinical entity is present. In
a longitudinal study of non-demented elderly
patients, 8.5% had a vitamin B12 level of 200 pg/
ml or less (6). In another study of depressed outpatients,
12% were found to have vitamin B12
levels of 200 pg/ml or less (7). Finally, in a study of
patients in a general medical hospital with mood
and cognitive disorders, 31.3% of those with a
mood disorder and 20.6% of those with a cognitive
disorder were found to have vitamin B12 levels less
than 400 pg/ml (8).
Finally, there needs to be an increase in the
urgency in the treatment of vitamin B12 deficiency.
While some clinicians may wish to undertake a
lengthy work-up to find the cause of the deficiency,
one must also remember that vitamin B12-induced
psychiatric illness must be corrected within
12 months or the damage may become irreversible
(9). It is felt that the most robust response occurs if
the patient’s vitamin B12 deficiency is corrected
within the first 6 months (9).
