Anemia is the medical term for a low red blood cell count. The bone marrow produces red blood cells (RBCs), which normally remain in the circulation for approximately three months. Diseases that decrease RBC production or shorten their lifespan in the circulation cause anemia. Inherited and acquired diseases can cause anemia.
Sickle Cell Anemia
Sickle cell anemia is an inherited disorder that causes abnormally-shaped RBCs. The RBCs are sickle or crescent shaped due to abnormal hemoglobin within the cells. The spleen removes old and defective RBCs from the circulation. Because they are abnormally shaped, sickle cells are removed from the circulation much more quickly than normal RBCs. This causes chronic anemia because the bone marrow is unable to produce sufficient RBCs to keep up with their rapid destruction by the spleen.
Thalassemias
Thalassemias are inherited disorders that cause structural abnormalities of the hemoglobin contained in RBCs. Different genetic abnormalities cause varying forms of thalassemia. However, all thalassemias cause a low red blood cell count. As with sickle cell anemia, the RBCs in people with thalassemia have a shortened life span in the circulation, leading to chronic anemia.
Pernicious Anemia
Pernicious anemia (also called megaloblastic anemia) is caused by a deficiency of intrinsic factor. The stomach produces intrinsic factor, which is necessary for the absorption of vitamin B-12 from the diet. With pernicious anemia, the immune system mistakenly destroys the cells that produce intrinsic factor, causing a vitamin B-12 deficiency. Because vitamin B-12 is required for RBC production, a deficiency causes decreased RBC formation and anemia. Vitamin B-12 shots can restore normal RBC production and reverse the anemia.
Chronic Kidney Disease
The kidneys produce the hormone erythropoietin, which stimulates RBC production by the bone marrow. With chronic kidney disease, erythropoietin production is impaired leading to reduced RBC production. As a result, people with chronic kidney disease typically have severe anemia.
Leukemia
White blood cell cancers are termed leukemias. Rapid division of leukemic cells in the bone marrow causes them to overtake normal bone marrow cells that produce RBCs. Thus, RBC production is decreased causing anemia.
Aplastic Anemia
Aplastic anemia is an uncommon condition in which the bone marrow fails to produce blood cells. The numbers of RBCs, white blood cells and platelets in the circulation fall to critically low levels. Frequent blood transfusions replace the absent blood cells.
Fanconi Anemia
Fanconi anemia is a rare genetic condition that causes bone marrow failure. The genetic abnormalities of Fanconi anemia cause defects in the cells that give rise to RBCs, white blood cells and platelets. Over time, the bone marrow fails, resulting in marked anemia along with low levels of white blood cells and platelets.
