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Diagnosis and treatment of vitamin B12 and folate deficiency

Stanley L Schrier, MD
Section Editor
William C Mentzer, MD
Deputy Editor
Jennifer S Tirnauer, MD


The diagnostic evaluation and treatment of the patient with suspected vitamin B12 (cobalamin, Cbl) or folate deficiency will be reviewed here. The causes of these deficiencies, their symptoms, and the mechanisms by which these vitamin deficiencies produce clinical abnormalities are discussed separately. (See "Etiology and clinical manifestations of vitamin B12 and folate deficiency" and "Physiology of vitamin B12 and folate deficiency".)

The terms "folate" and "folic acid" are sometimes used interchangeably; however, the vitamin is found in nature as a folate while folic acid (FA) is the synthetic, therapeutic form of the vitamin.


Classical presentation — In the "classic" advanced case of vitamin B12 or folate deficiency, the patient presents with severe anemia and macrocytic red cells (mean corpuscular volume (MCV) >100 fL) with or without varying neurologic disturbances.

However, many patients with vitamin B12 deficiency exist who have no or only mild anemia, and macrocytosis may be masked by a concurrent disorder (eg, iron deficiency, thalassemia). In one series, for example, the diagnosis of vitamin B12 deficiency was confirmed in patients in whom only 29 percent had anemia, and only 36 percent had an MCV >100 fL [1].

Hypersegmentation of neutrophils, if present, should suggest the diagnosis of B12 or folate deficiency, particularly in patients who also have neurologic symptoms, even in the absence of anemia. (See "Etiology and clinical manifestations of vitamin B12 and folate deficiency".)


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Literature review current through: Mar 2017. | This topic last updated: Sep 21, 2016.
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