Microcytosis is the frequent occurrence of microcytes. These are erythrocytes with a diameter less than 6 µm and a MCV > fl in which the central pallor is still visible.

The nucleus of a normal lymphocyte has a diameter of about 8.5 µm, the erythrocyte has a diameter of about 7 µm. Therefore, it can help to determine the size of erythrocytes by comparing them to the nucleus of small lymphocytes. In general, the erythrocytes of children are smaller. In neonates, erythrocytes are larger, a microcytosis is rarely present. Consequently, age specific normal values have to be considered.


Microcytosis occurs in disorders of hemoglobin synthesis such as iron deficiency anemia or thalassemia