What Causes Red Blood Cells to Be Small in Size?

Microcytic anemia is the condition wherein red blood cells are smaller than normal, and it is primarily caused by iron deficiency anemia and thalassemia, according to Dr. Siamak T. Nabili writing for eMedicineHealth. Iron deficiency anemia occurs due to limited or inadequate iron intake.

Dr. Nabili explains that the bone marrow requires a sufficient supply of iron to produce red blood cells. People with poor dietary intake usually suffer from iron deficiency anemia as they do not have the required amount of iron. Stomach ulcers or conditions that cause slow, chronic bleeding also lead to iron deficiency anemia as iron is lost from the body at a high rate due to chronic, ongoing and slow blood loss.

Thalassemia is a hereditary blood disorder wherein the body creates an abnormal form of hemoglobin, the protein contained in red blood cells that transports oxygen, according to MedlinePlus. It causes excessive destruction of red blood cells, leading to anemia. The two major types of thalassemia are alpha thalassemia, which occurs when genes related to the alpha globin protein are missing or mutated, and beta thalassemia, which occurs when gene defects change the production of the beta globin protein. People with minor forms of the alpha and beta thalassemia have smaller red blood cells than normal; however, they do not experience usual symptoms, like fatigue, growth failure and facial bone deformities.