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What is sickle cell disease?

Sickle cell disease is an inherited blood disorder characterized by defective hemoglobin, a protein in red blood cells that carries oxygen to the tissues of the body.

Sickle cell disease involves the red blood cells, or hemoglobin in them, and their ability to carry oxygen. Cells with normal hemoglobin are smooth, round and flexible, like the letter “O,” so they can move through the vessels in our bodies easily. Sickle-cell affected red blood cells are stiff and sticky, and form into the shape of a sickle, or the letter “C,” when they lose their oxygen. These sickled cells tend to cluster together and cannot easily move through the blood vessels. The cluster causes a blockage and stops the movement of healthy, normal oxygen-carrying blood. This blockage is what causes the painful and damaging complications of sickle cell disease.

Sickle cells only live for about 10 to 20 days, while normal cells can live up to 120 days. Also, sickle cells risk being destroyed by the spleen because of their shape and stiffness. The spleen is an organ that helps filter the blood of infections, and sickled cells get stuck in this filter and die. Due to the decreased number of hemoglobin cells circulating in the body, a person with sickle cell disease is chronically anemic. The spleen also suffers damage from the sickled cells blocking healthy oxygen-carrying cells. Without a normal functioning spleen, these individuals are more at risk for infections. Infants and young children are at risk for life-threatening infections.

The most common variations of the sickle cell gene include the following:

  • Sickle cell trait
    The person is carrying the defective gene, HbS, but also has some normal hemoglobin, HbA. This is referred to as HbAS. Persons with sickle cell trait are usually without symptoms of the disease. Mild anemia may occur. Under intense, stressful conditions, exhaustion, hypoxia (low oxygen) and/or severe infection, the sickling caused the defective hemoglobin may occur and result in some complications associated with the sickle cell disease.
  • Sickle cell anemia
    The person has most or all of the normal hemoglobin (HbA) replaced with the sickle hemoglobin (HbS). This is referred to as HbSS. It is the most common and most severe form of the sickle cell variations. These persons suffer from a variety of complications due to the shape and thickness of the sickled cells. Severe and chronic anemia also is a common characteristic for children with HbSS.
  • Sickle cell-hemoglobin C disease
    The person has both HbS and HbC. This is often referred to as HbSC. Hemoglobin C causes red blood cells, called target cells, to develop. Having just some hemoglobin C and normal hemoglobin, a person will not have any symptoms of anemia. However, if the sickle hemoglobin S is combined with the target cell, some mild to moderate anemia may occur. These persons often suffer some of the complications associated with HbSS sickle cell disease, but to a milder degree. Vasoocclusive crises (the flow of blood is blocked because the sickled cells have become stuck in the blood vessels), organ damage from repeated sickling and anemia and high risk for infection are all similar traits for HbSS and HbSC.
  • Sickle cell-hemoglobin E disease
    This variation is similar to sickle cell-C disease except that an element has been replaced in the hemoglobin molecule. This variation also is often seen in Southeast Asian populations. Some persons with hemoglobin E disease are without symptoms. However, under certain conditions, such as exhaustion, hypoxia, severe infection and/or iron deficiency, some mild to moderate anemia may occur.
  • Hemoglobin S-beta-thalassemia
    This involves an inheritance of both the thalassemia and sickle cell genes. The disorder produces symptoms of moderate anemia and many of the same conditions associated with sickle cell disease. While this disorder more often has milder symptoms than sickle cell disease, it also may produce exacerbations as severe as those of sickle cell disease.

All forms of sickle cell disease can exhibit the complications associated with the disease.

Who is affected by sickle cell disease?

Sickle cell disease primarily affects those of African descent and Hispanics of Caribbean ancestry, but the trait also has been found in those with Middle Eastern, Indian, Latin American, Native American and Mediterranean heritage.  It has been estimated that more than 72,000 people in the U.S. are affected by the disease and that millions worldwide suffer complications from sickle cell disease.

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