•Microcytic red blood cells measure 6 microns or less in diameter.  The mean corpuscular volume is generally less than 80 fL, though the normal range varies slightly between laboratories and in different age groups.  In contrast to spherocytes, which are also decreased in diameter, microcytes retain their central pallor.  In microcytosis due to iron deficiency, the central pallor is increased (more than 1/3 the diameter of the cell).