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Tests for Vitamin B12 Deficiency:
Often a serum vitamin B12 is ordered in assessment of a patient's nutritional condition. One difficulty with vitamin B12 levels are that low levels are neither specific or sensitive for vitamin B12 deficiency. "Low normal" levels of vitamin B12 have been associated with anemia and with neurological disease. Recently there has been interest in measuring levels of serum homocysteine and methylmalonic acids. These precursors build up in vitamin B12 deficiency and appear to be better measure of tissue vitamin B12 deficiency. Increased levels of homocysteine and methylmalonic acid also are better able to predict neurological and hematological response to vitamin B12 therapy.
Vitamin B12 and the elderly
On routine screen as many as 10-23% of elderly patients will have low vitamin B12 levels. One study found that 14.5% had levels below 300 pg/ml with 56% of these patients having increased levels of homocysteine and methylmalonic acid indicative of tissue vitamin B12 deficiency. The most common mechanism is inability to absorb vitamin B12 from food. These patient will often have normal Schilling's tests. It is speculated the rapid rise in the use of H2 blockers will increase this problem in this patient population. Patients with dementia have lower levels of vitamin B12 then those without but treatment with vitamin B12 is often not effective, perhaps due to the duration of the neurological damage.
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Food-Cobalamin Malabsorption:
In this case, patient may have a normal Schilling test but vitamin B12 levels are low!
Failure to absorb food-based vitamin B12!
It has a variable cours and may progress to pernicous anemia. It may reverse with antibiotics.
This condition may be encountered in patients who are taking proton-pump inhibitors. May also be seen on post-gastrectomy states.
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