Macrocytes have a diameter of 9-14 microns (1 1/2 to 2 times larger than normal red cells) and the MCV is 100 cubic microns or more. The macrocytes seen in this slide are referred to as true macrocytes, or megalocytes. Compare the red cells in the field to the nucleus of the lymphocyte in the lower left. Many of the red cells in the field are larger than the lymphocyte and have little or no central pallor. As a point of reference, the cells just below and above the lymphocyte are macrocytes. Megalocytes are frequently oval and several examples of oval macrocytes can be seen in this field. Megalocytes are the result of decreased deoxyribonucleic acid (DNA) synthesis, frequently due to vitamin B12 and/or folic acid deficiencies. Decreased DNA synthesis causes the nucleus in the developing red cells to mature at a slower than normal rate. Since hemoglobin production is not affected, the mature red cell is larger than normal is filled with hemoglobin.