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February 26, 1982

Vitamin B12 Deficiency and Early Rise in Mean Corpuscular Volume-Reply

JAMA. 1982;247(8):1126. doi:10.1001/jama.1982.03320330022014

In Reply.—  The observations of Drs Smith and Malon support my earlier statements that "deficiencies of vitamin B12 or folate are among the least common causes of a high MCV," and "the MCV is a clue to the possibility of vitamin B12... or of folate deficiency." The rewards of an early diagnosis are high and the physician should not ignore this simple clue that comes as a "gift" when he requests a complete blood cell count from a laboratory.Neither the serum vitamin B12 level nor the serum folate level should ever be relied on as the sole means of establishing the presence of a deficiency of the respective vitamin.1-3 The assays were developed, evaluated, and introduced by interested physicians as aids in the differential diagnosis of megaloblastic anemias. The subsequent adoption by hospital laboratories everywhere and the totally misdirected and wasteful applications as screens in