Red blood cells contain hemoglobin, a protein that carries oxygen in the blood. Normal red blood cells are round and flexible, which enables them to travel through small blood vessels to deliver oxygen to all parts of the body.
Sickle cell disease causes red blood cells to form into a crescent shape, like a sickle. The sickle-shaped red blood cells break apart easily, causing anemia. Sickle red blood cells live only 10-20 days instead of the normal 120 days. The damaged sickle red blood cells also clump together and stick to the walls of blood vessels, blocking blood flow. This can cause severe pain and permanent damage to the brain, heart, lungs, kidneys, liver, bones, and spleen. Severe pain is an emergency called acute sickle cell crisis. A person may not know what brought on the pain, but infection and dehydration are common triggers.
Sickle cell disease is most common in Africans and African-Americans. It is also found in other ethnic and racial groups, including people from South and Central America, the Caribbean, Mediterranean countries, and India.
What Causes Sickle Cell Disease?
Sickle cell disease is caused by a genetic abnormality in the gene for hemoglobin, which results in the production of sickle hemoglobin. When oxygen is released from sickle hemoglobin, it sticks together and forms long rods, which damage and change the shape of the red blood cell. The sickle red blood cells causes the symptoms of sickle cell disease.
Children are born with sickle cell disease; it is not contagious. It occurs when a child inherits two sickle hemoglobin genes, one from each parent. About 2,000 babies are born with sickle cell disease each year in the United States. People who inherit only one sickle hemoglobin gene are carriers (sickle cell trait) and do not have anemia or painful sickle cell crises. They may, though, have a slightly higher incidence of certain conditions such as blood in the urine or urinary tract infections. About 2 million Americans have sickle cell trait.
What Are the Symptoms of Sickle Cell Crisis?
Symptoms of sickle cell crisis include:
- Severe pain
- Chest pain and difficulty breathing
- Joint pain and arthritis and bone infarctions
- Blockage of blood flow in the spleen or liver
- Severe infections
Patients with sickle cell disease may develop severe pain in the chest, back, arms, legs, and abdomen. Pain can occur anywhere in the body. Sickle red blood cells in the lungs can cause severe illness with chest pain, fever, and difficulty breathing. Sickle cell disease can also cause permanent damage to the brain, heart, kidneys, liver, spleen, and bones. The severity and symptoms vary greatly from person to person, even within the same family.
How Is Sickle Cell Disease Diagnosed?
Sickle-shaped red blood cells can be seen when a blood sample is examined under a microscope. But sickle cell disease is diagnosed by a blood test called hemoglobin electrophoresis, which measures the amount of the abnormal sickle hemoglobin. The amount of sickle hemoglobin determines whether the person is a carrier (sickle cell trait) or has sickle cell disease.
There are also rapid screening tests that detect the formation of sickle red blood cells or clumps of abnormal sickle hemoglobin when oxygen is removed from the blood. These tests are less commonly used, because they cannot distinguish between sickle cell trait and sickle cell disease.
Testing newborns for sickle cell disease is required by law in all 50 states. Early detection and treatment reduces the risk of serious infections and other complications.
How Is Sickle Cell Disease Treated?
Treatment of sickle cell crisis includes:
- Opioid pain medications (for example, morphine)
- Anti-inflammatory medications (for example, ibuprofen)
- Antibiotics for infection
- Intravenous or oral fluids
Transfusions of red blood cells are given for severe anemia, to prevent strokes, and before surgery. Sometimes an exchange transfusion is performed with a special machine that removes the abnormal sickle red blood cells and replaces them with normal red blood cells.
Hydroxyurea is the only FDA-approved medication that prevents painful episodes in sickle cell disease. Studies of patients with sickle cell disease show that the regular use of hydroxyurea decreases the frequency and severity of sickle cell crises and reduces the number of blood transfusions and hospitalizations.
Stem cell transplant is the only curative treatment for sickle cell disease. More than 200 patients with sickle cell disease have undergone stem cell transplants from a matched sibling donor. Stem cell transplant has a 5%-10% risk of death, but patients with successful transplants were completely cured of sickle cell disease, with no further episodes of pain.
Stem cell transplant is performed in young patients with severe sickle cell disease who have a matched sibling donor. Stem cell transplant using umbilical cord blood from a related donor has also been curative in a small number of patients.
Scientists are making progress in the development of new medications that prevent sickling of red blood cells and improve blood flow and delivery of oxygen to the body. Some of these new treatments are already being tested in patients with sickle cell disease.
What Is the Outlook for People With Sickle Cell Disease?
People who have sickle cell disease have a reduced life expectancy. But because of improvements in treatment, people with sickle cell disease now live longer and have a better quality of life. In 1973, the average life span was 14, but people with sickle cell disease now live into their 40s and 50s, and in some cases, beyond the age of 60. Long-term treatment with hydroxyurea may prolong survival.