Sickle cell anemia, also called HbSS, is the most common type of sickle cell disease. Sickle cell diseases are serious genetic (hereditary) conditions in which the red blood cells are sickle- or crescent-shaped. (Normal red blood cells are disc-shaped.) Other forms of sickle cell disease include HbSC and HbS beta thalassemia.

Sickle cell anemia is an inherited disorder that is present at birth and lifelong. People with sickle cell anemia have two sickle cell genes—one from each parent. People who inherit one sickle cell gene and one healthy gene have sickle cell trait.

Healthy red blood cells contain iron-rich hemoglobin that carries oxygen throughout the body. Sickle cells contain an abnormal hemoglobin protein called hemoglobin S and are stickier and harder than normal red blood cells. Sickle cells block the flow of blood through the blood vessels, resulting in pain, organ damage, and an increased risk for infection.

Also, while healthy red blood cells live about 120 days, sickle cells die after only about 10 to 20 days. In people with sickle cell anemia, the bone marrow is unable to manufacture new red blood cells fast enough—causing a shortage of red blood cells.

People with sickle cell trait produce both normal red blood cells and sickle cells. They may pass the gene for the disorder on to their offspring, but usually don’t develop symptoms. Some people with sickle cell trait develop medical complications that may be related to the defective gene.

Risk Factors for Sickle Cell Anemia

According to the National Heart, Lung, and Blood Institute of the National Institutes of Health (NIH), sickle cell anemia affects about 70,000–100,000 people and sickle cell trait affects about 2 million people in the United States. Sickle cell anemia is most common in African Americans, affecting about 1 in 500. It also affects Hispanic Americans, affecting more than 1 in 36,000. Sickle cell trait affects about 1 in 12 African Americans in the United States.

People whose family comes from certain areas of the world are at increased risk for sickle cell anemia. These areas include the following:

  • Africa
  • the Caribbean Islands
  • Central America (especially Panama)
  • the Mediterranean (Greece, Italy, Turkey)
  • India
  • Saudi Arabia
  • South America

Sources: National Heart, Lung, and Blood Institute of the National Institutes of Health (NIH); U.S. Centers for Disease Control and Prevention (CDC)

Publication Review By: the Editorial Staff at

Published: 16 Jul 2014

Last Modified: 16 Jul 2014