Neurological disease associated with vitamin B12 deficiency may be irreversible; therefore, early detection is critical in preventing permanent neurological damage.
Traditionally, the diagnosis of vitamin B12 deficiency relied on the finding of low serum vitamin B12 (generally, <148 picomols/L [<200 picograms/mL]) and clinical symptoms consistent with vitamin B12 deficiency. However, markers of tissue deficiency such as homocysteine, methylmalonic acid (MMA), and holotranscobalamin have improved earlier diagnosis of vitamin B12 deficiency. Optimal use of serum vitamin B12 and tissue markers is undefined, but general guidance will help the clinician to determine whether a patient has true vitamin B12 deficiency.
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