Human blood smear showing sickle cell anemia. Sickle cell anemia is an inherited blood disease in which the red blood cells contain abnormal hemoglobin, the oxygen-carrying pigment. During deoxygenation, the hemoglobin distorts the red blood cells into a sickle shape, causing bone ache and organ damage. The fragile sickle cells are easily destroyed in the bloodstream. There is no effective cure, and treatment aims to alleviate the symptoms.