Red blood cells, also called erythrocytes, carry oxygen from the lungs throughout the body using the circulatory system. Various medical conditions can affect these cells, causing small red blood cells, enlarged red blood cells, and also affecting their shape and color. The most common cause of small cells is iron deficiency anemia, which is usually a result of insufficient iron intake, excessive bleeding, or problems with iron absorption. The medical term used when it is caused by anemia is microcytic anemia, and treatment varies depending on the underlying cause. There are also some rare blood disorders that can cause small red blood cells such as spherocytosis, various forms of thalassemia, and sideroblastic anemia.
Anemia and other blood disorders are commonly diagnosed using a complete blood count, or CBC. This blood test examines the red blood cells in detail, using several red blood cell indices. For example, the number of blood cells and the variation in their size is noted. In order to ensure proper diagnosis and treatment, it is important to consult a medical professional if a blood test shows small red blood cells.
Iron deficiency anemia is usually caused by a lack of iron in the diet; by blood loss, for example from a stomach ulcer or childbirth; or by poor iron absorption, sometimes caused by intestinals disorders like Crohn's disease or celiac disease. A lack of iron causes fewer red blood cells to be produced, and the cells that are formed are small and pale due to the lack of hemoglobin. Hemoglobin is what gives red blood cells their color, and it is also what makes them able to carry oxygen. Iron is essential for the formation of hemoglobin. The most common treatment for iron deficiency anemia is iron supplements, but other medications are sometimes needed to treat the cause.
Other blood disorders can also cause small red blood cells, though these conditions are rare. One example is sideroblastic anemia, which is not caused by a lack of iron but by problems with the body's hemoglobin production, resulting in fewer red blood cells that are small in size and pale in color. Spherocytosis is another rare genetic blood disorder that causes red blood cells to be small as well as abnormal in shape. Various forms of thalassemia, sometimes called Cooley's anemia, can also cause small, pale, and fragile red blood cells. Thalassemias are usually inherited and vary in severity.