Megalocyte Information and Courses from MediaLab, Inc.

Another type of macrocyte can be seen in the center of this slide. Notice it appears larger than the lymphocyte but in contrast to megalocytes has an area of central pallor. These macrocytes are sometimes referred to as "pseudo macrocytes," since their size is the result of exaggerated flattening (leptocyte) and thus the presence of the central pallor. The MCV for this type of macrocyte is within normal range. Pseudomacrocytes can be seen in patients with cirrhosis of the liver, obstructive jaundice, post splenectomy and conditions that affect the red cell membrane.

To summarize, two types of macrocytes can be seen, true macrocytes (megalocytes) and pseudomacrocytes. The MCV and MCH values will be increased when megalocytes are present, while all the indice values will be normal when pseudomacrocytes are found.

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.

A decreased amount of hemoglobin is referred to as hypochromasia or hypochromia. MCHC values of 30% or less reflect this condition. Hyperchromasia and hyperchromia, refer to a hypothetical situation rather than an actual occurrence. The word, hyperchromia/sia, means increase in color; however the MCHC value cannot be higher than 36, since it is impossible for a cell to contain "too much" hemoglobin.Cells located in the "too thin" portion of the smear often appear to be "hyperchromic". Megalocytes (macrocytes), which appear to have increased amounts of hemoglobin, have an MCHC value within normal limits, indicating that the cells, although larger than normal, are normochromic.