- Last Update On : 2013-03-02
Macrocytic anemia, glossitis, peripheral neuropathy, weakness, hyperreflexia, ataxia, and other neurological manifestations characterize classical vitamin B12 (cobalamin) deficiency. It is common, however, to encounter patients with vitamin B12 deficiency who have atypical clinical or laboratory features. For example, many patients present with neurological defects without macrocytic anemia. Assay of serum vitamin B12, widely used as a screening test for cobalamin deficiency, has significant problems regarding sensitivity and specificity. A falsely low serum vitamin B12 level may be seen in the absence of true deficiency, and conversely neurological manifestations of vitamin B12 deficiency may be present despite normal or minimally depressed serum vitamin B12 levels.
Several laboratory tests can assist in the diagnosis of vitamin B12 deficiency and pernicious anemia. The accompanying algorithm describes an approach to this problem using the following tests: