What is sickle cell anemia? Sickle cell anemia is an inherited disease of the red blood cells. Normally red blood cells contain a protein called hemoglobin A, which carries oxygen to all organs in the body. With sickle cell anemia, however, the body produces a different type of protein, called hemoglobin S. The problem is that when a red blood cell with hemoglobin S releases oxygen, the cell changes from the usual donut shape to a sickle or S-shape , and becomes stiff rather than soft and flexible like normal red blood cells. This "sickle cell", which looks like a crescent moon, cannot continue to slide through the small blood vessels as usual. Instead, it gets stuck in tiny blood vessels, blocking blood flow and causing pain. The spleen, an organ on the left side of the abdomen in front of the liver, is responsible for filtering the blood for infections and other abnormalities. Normal red blood cells can change shape and pass through this filter, but sickle cells get stuck and can't recirculate through the body, so the number of circulating blood cells decreases. Meanwhile, the bone marrow, where red blood cells are produced, steps in to produce more cells. However, it cannot keep up with the destruction, so the total number of red blood cells drops to a low level and the body becomes anemic. (“Anemic” is the medical word for having a low red blood cell count.) What is sickle cell anemia? Sickle cell anemia is an inherited disease of the red blood cells. Normally red blood cells contain a protein called hemoglobin A, which carries oxygen to all organs in the body. With sickle cell anemia, however, the body produces a different type of protein, called hemoglobin S. The problem is that when a red blood cell with hemoglobin S releases oxygen, the cell changes from the usual donut shape to a sickle or S-shape , and becomes stiff rather than soft and flexible like normal red blood cells. This "sickle cell", which looks like a crescent moon, cannot continue to slide through the small blood vessels as usual. Instead, it gets stuck in tiny blood vessels, blocking blood flow and causing pain. The spleen, an organ on the left side of the abdomen in front of the liver, is responsible for filtering the blood for infections and other abnormalities..