Diagnosing Vitamin B12 and/or Folate Deficiency



It turns out that simply measuring serum levels of B12 or folate is simply inadequate to diagnosis

deficiency. Up to 30% of people with low normal B12 levels will be deficient and many people with low B12

stores have normal tissue stores. A more reliable method is to assay for the metabolic products that

accumulate in B12 deficiency. Since B12 is involved in conversion of homocysteine to methionine, lack of B12

will lead to elevated homocysteine level. Also B12 is involved in conversion of methylmalonic acid to succinyl

so in B12 deficiency, methylmalonic acid accumulates. Both homocysteine and methylmalonic acid assays

are widely available and should be the first line tests for B12 deficiency.



Serum folate levels are also very unreliable. Since folate is needed for conversion of homocysteine

to methionine, serum homocysteine will also accumulate in folate deficiency and is a more sensitive marker

of tissue folate stores.



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