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Vitamin B-12 deficiency can be difficult to diagnose clinically,
as its symptoms are often nonspecific including:
- Fatigue
- Lassitude
- Malaise
- Vertigo
- Cognitive impairment that could be attributed to old age
Moreover, symptoms vary and often don’t include the classic
signals such as:
- macrocytic anemia
- peripheral neuropathy
- subacute combined degeneration of the spinal cord
Standard tests to assess vitamin B-12 concentrations are limited
because the clinical severity of vitamin B-12 deficiency is unrelated
to vitamin B-12 concentrations.
Accurate identification of vitamin B-12 deficiency is important
for a number of reasons. For example, macrocytic anemia, which can
be a signal of vitamin B-12 deficiency, may also be caused by folate
deficiency. The anemia may have different neurologic features depending
on the cause. Therefore, inappropriately treating the condition
with folic acid will correct the hematologic signs of vitamin B-12
deficiency but will not address the neurologic symptoms.
Vitamin B-12 deficiency results in elevated serum concentrations
of methylmalonic acid (MMA); therefore elevated concentrations of
MMA have been suggested to indicate vitamin B-12 deficiency.
However, there is no consensus on cut-off levels of MMA to use
to define vitamin B-12 deficiency among elderly people. Among this
group, impaired renal function can be an important confounding factor.
Both vitamin B-12 deficiency and folate deficiency are common among
older people.
In one study, MMA of less than 200 pmol/L was used to define individuals
as being at high risk of vitamin B-12 deficiency.
However, 15 percent to 30 percent of people with high vitamin B-12
concentrations also had elevated MMA concentrations, which indicates
that elevated MMA is not always a reliable indicator.
Instead, the ultimate indicator for vitamin B-12 deficiency may
be the reduction in MMA concentrations and improvement in clinical
symptoms after being treated with vitamin B-12.
Researchers gave the following recommendation for a more reliable
screening of vitamin B-12 deficiency: If vitamin B-12 concentration
is less than 150 pmol/L, more detailed investigation is required
to find an underlying cause and treatment. If vitamin B-12 concentration
is between 150 and 200 pmol/L, then use of MMA may help to identify
those who require more detailed investigation and treatment.
American
Journal of Clinical Nutrition May, 2003;77(5):1241-7 (Free Full
Text Article)
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