To the Editor.—
In the article by Charles A. Hall, MD (1981;245:1144), we do not dispute the fact that a high mean corpuscular volume (MCV) (normal range, 78 to 93 femtoliters [fL]) should alert a physician to the possibility of vitamin B12 or folate deficiency; however, there are a multitude of other important causes of high MCV, some of which are liver disease, renal disease, hypothyroidism, blood regeneration, and malaria, to name a few.1In our experience, which consists of a study of the vitamin B12 status of 772 patients during a two-year period, 101 (13%) were found to have a low serum vitamin B12 level. Of these 101 patients only four were found to have a high MCV (greater than 93 fL).Conversely, in 45 patients of the 772 studied who had a high MCV, only five (11%) had a low vitamin B12 serum
Smith TJS, Malon RG. Vitamin B12 Deficiency and Early Rise in Mean Corpuscular Volume. JAMA. 1982;247(8):1126. doi:10.1001/jama.1982.03320330022013
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