<P> Deficiencies of Vitamin B or folate produce a macrocytic anemia (large cell anemia) in which the RDW is elevated in roughly two - thirds of all cases . However, a varied size distribution of red blood cells is a hallmark of iron deficiency anemia, and as such shows an increased RDW in virtually all cases . In the case of both iron and B deficiencies, there will normally be a mix of both large cells and small cells, causing the RDW to be elevated . An elevated RDW (red blood cells of unequal sizes) is known as anisocytosis . </P> <P> An elevation in the RDW is not characteristic of all anemias . Anemia of chronic disease, hereditary spherocytosis, acute blood loss, aplastic anemia (anemia resulting from an inability of the bone marrow to produce red blood cells), and certain hereditary hemoglobinopathies (including some cases of thalassemia minor) may all present with a normal RDW . </P> <P> The "width" in RDW - CV is sometimes thought to be "misleading," since it in fact is a measure of deviation of the volume of RBCs, and not directly the diameter . However, "width" refers to the width of the volume curve (distribution width, here presented as the Coefficient of Variation, or CV), not the width of the cells . Thus, it is a reasonably accurate term . </P> <P> Mathematically, the RDW - CV is calculated with the following formula: </P>

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