Q. I’m having some difficulty grasping the MCHC, MCV and RDW in hereditary spherocytosis. Wouldn’t the MCHC, MCV, and RDW be elevated in all anemias? What makes hereditary spherocytosis special?

A. MCHC, MCV and RDW aren’t elevated in all anemias…they are different in different anemias.

The mean cell volume (MCV) tells you whether cells are small (microcytic), normal (normocytic) or big (macrocytic). The mean cell hemoglobin concentration (MCHC) tells you how much hemoglobin there is on average in a red cell. If the MCHC is low, the cells are called hypochromic. If the MCHC is normal, the red cells are called normochromic. The MCHC doesn’t ever go above normal (so there isn’t such a thing as a macrochromic cell!).

The red cell distribution width (RDW) tells you how much the red cells vary in size from one to another. If the red cells are all pretty much the same size, the RDW is within the normal range. If there some small red cells and some large red cells, the RDW is increased (the word for this variation in red cell size is anisocytosis).

In hereditary spherocytosis, the MCV is generally normal. The anemias in which the MCV is low include iron-deficiency anemia and thalassemia. Anemias in which the MCV is elevated include megaloblastic anemia and a few other types of anemias including alcohol-related anemia. Most other anemias are just normocytic.

In hereditary spherocytosis, the MCHC and RDW are also usually normal. The red cells are normochromic and there is minimal anisocytosis. Basically, all you see are a bunch of spherocytes (these are the darker-appearing red cells with no central pallor in the image above)…and that doesn’t much change any of these parameters.