What is sickle cell disease?

Sickle cell disease is the term given to inherited blood cell disorders that develop in individuals with abnormal hemoglobin in their red blood cells.

Nearly 100,000 people in the United States have some form of sickle cell disease, which is passed by genes from parents to children.

The majority of sickle cell disease cases occur in black individuals, and the severity varies greatly from person to person.

The most common — and most severe — form is sickle cell anemia.

Sickle cell anemia occurs when there are two hemoglobin S genes, dubbed Hemoglobin SS. Sickle cell anemia symptoms include anemia, pain episodes, hand–foot syndrome, vision problems, delayed growth and frequent infections. A sickle cell crisis — a painful episode that occurs in individuals with sickle cell anemia — occurs when sickle-shaped red blood cells block blood vessels. Pain arises when blood and oxygen cannot reach body tissue.

Other common forms of sickle cell disease are hemoglobin SC disease and hemoglobin S thalassemia.

Individuals who inherit one sickle cell gene and one normal gene have a condition known as sickle cell trait. These individuals typically do not have any symptoms of sickle cell disease, but they can pass the trait on to their children.

Condition overview

Oxygen is carried throughout the body via hemoglobin protein in red blood cells.

Red blood cells that consist of normal hemoglobin are shaped like a disc, which allows the cells to move easily through large and small blood vessels to deliver oxygen.

Sickle cell hemoglobin can form stiff rods within the red blood cell, thus changing the shape into a crescent form, or sickle shape.

These stiff rods are not flexible and can attach to vessel walls, leading to a blockage that slows or halts blood flow. Oxygen, therefore, cannot reach nearby tissues.

The lack of oxygen is associated with sudden onset of severe pain, known as pain crises. When a person with sickle cell disease experiences these sudden attacks, they most often will require treatment at a hospital.

Symptoms and complications

Sickle cell disease is apparent at birth. Every U.S. state, the District of Columbia and U.S. territories require all newborns to be tested for sickle cell disease.

Although adolescents and adults may suffer from chronic ongoing pain, most young children with sickle cell disease remain pain free between pain crises episodes.

Early symptoms include dactylitis, fatigue and jaundice, or a yellowish tone of the skin or whites of the eyes. Over time, the bones, brain, eyes, heart, joints, kidneys, liver, lungs, penis, skin or spleen may be harmed by the red cell sickling and poor levels of oxygen throughout the body.

The lifetime of sickle cells is only about 10 to 20 days, whereas normal red blood cells thrive between 90 and 120 days. This is because sickle cells are unable to change their shape easily and burst apart or hemolyze.

A person with sickle cell disease has a lower red blood cell count, which can lead to anemia and lethargy.

Treatment and outcomes

Advances in the diagnosis and care of sickle cell disease have improved the lifespan of those with sickle cell disease during the past few decades. The current average life expectancy of a person living with sickle cell disease in the United States is between 40 and 60 years.

Effective treatments reduce symptoms and extend life; early diagnosis and regular follow-up care can prevent potential complications. Moreover, practicing a healthy lifestyle — including eating a healthy diet, getting plenty of sleep and regular physical activity — help to prevent and control complications.

An NHLBI expert guideline recommends hydroxyurea be offered to all children with hemoglobin SS and S sickle cell disease, and that it be considered an option for children with clinically severe hemoglobin SC and S+ disease genotypes.

Although hematopoietic stem cell transplantation is the only potential cure, a well-matched donor is required for a successful transplant and most people do not have a relative who is a good enough donor match. Age also can be a prohibitive factor for transplant.

Research is underway to try to improve stem cell transplants for adults with sickle cell disease, as well as identify how genes and other risk factors contribute to pain crises.

Information on current ongoing clinical trials can be found at: www.nhlbi.nih.gov/health/health-topics/topics/sca/trials.

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