Masked macrocytosis and the use of serum vitamin B12 and folate assays1

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A case of “masked” macrocytosis in an iron and folate deficient male alcoholic is presented. Reliance on algorithms based on mean corpuscular volume (MCV) values for decision-making in the workup of anemic patients may, occasionally, produce diagnostic difficulties, and combination deficiencies or concomitant disease states may affect test interpretation. Appropriate use of radioisotopic dilution assays for vitamin B12 and folate depends on careful clinical observation, blood count, and screening examination of the peripheral smear before confirmatory tests are ordered.



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