Sickle cell disease is a group of inherited red blood cell disorders that affects hemoglobin, the protein that carries oxygen through the body. Normally, red blood cells are disc shaped and flexible to move easily through the blood vessels. If you have sickle cell disease, your red blood cells are crescent or “sickle” shaped. These cells do not bend and move easily and can block blood flow to the rest of your body.
The blocked blood flow through the body can lead to serious problems, including stroke, eye problems, infections and episodes of pain, called pain crises. Having sickle cell disease also raises your risk for severe illness from COVID-19. Learn steps you can take to help prevent infection from the Centers for Disease Control and Prevention.
Sickle cell disease is a lifelong illness. A blood and bone marrow transplant is currently the only cure for sickle cell disease, but there are effective treatments that can reduce symptoms and prolong life.
Your healthcare team will work with you on a treatment plan to reduce your symptoms and manage the condition. The NHLBI is leading and supporting research and clinical trials to find a cure for sickle cell disease.
People who have sickle cell disease have abnormal hemoglobin, called hemoglobin S or sickle hemoglobin, in their red blood cells. Hemoglobin is a protein in red blood cells that carries oxygen throughout the body. People who have sickle cell disease inherit two abnormal hemoglobin genes, one from each parent.
The types of sickle cell disease include the following:
In all types of sickle cell disease, at least one of the two abnormal genes causes a person’s body to make hemoglobin S. When a person has two hemoglobin S genes (hemoglobin SS), the disease is called sickle cell anemia. This is the most common and often most severe type of sickle cell disease. Hemoglobin SC disease and hemoglobin Sβ thalassemia are two other common types of sickle cell disease. Hemoglobin SD and hemoglobin SE are much less common.
Abnormal hemoglobin, called hemoglobin S, causes sickle cell disease.
Sickle cell disease is a genetic disorder caused by mutations in the beta globin gene that leads to faulty hemoglobin protein, called hemoglobin S. Hemoglobin S changes flexible red blood cells into rigid, sickle-shaped cells. These sickle cells can block blood flow, and result in pain and organ damage. Medical Animation Copyright © 2020 Nucleus Medical Media, All rights reserved.
Sickle cell disease is an inherited disease caused by defects, called mutations, in the beta globin gene that helps make hemoglobin. Normally, hemoglobin in red blood cells takes up oxygen in the lungs and carries it through the arteries to all the cells in the tissues of the body. Red blood cells that contain normal hemoglobin are disc-shaped and flexible so that they can move easily through large and small blood vessels to deliver oxygen.
Sickle hemoglobin is not like normal hemoglobin. The mutations in the gene cause a problem when oxygen levels in the blood are lower, which occurs once the hemoglobin has delivered oxygen to the cells in the body’s tissues. With less oxygen, the abnormal hemoglobin S gene can cause rigid, nonliquid protein strands to form within the red blood cell. These rigid strands can change the shape of the cell, causing the sickled red blood cell that gives the disease its name.
Sickle-shaped cells are not flexible and can stick to vessel walls, causing a blockage that slows or stops the flow of blood. When this happens, oxygen is unable to reach nearby tissues. The lack of oxygen in tissue can cause attacks of sudden severe pain, called pain crises. These pain attacks can occur without warning, and a person who has them often needs to go to the hospital for effective treatment.
Because sickle cells cannot change shape easily, they tend to burst apart. Normal red blood cells live about 90 to 120 days, but sickle cells last only 10 to 20 days. The body is always making new red blood cells to replace the old cells. However, in sickle cell disease, the body may have trouble keeping up with how fast the cells are being destroyed. Because of this, the number of red blood cells is usually lower than normal. This condition, called anemia, can cause a person to have less energy.
When the hemoglobin S gene is inherited from only one parent, and a normal hemoglobin gene—hemoglobin A—is inherited from the other, that person will have sickle cell trait. People who have sickle cell trait are generally healthy.
Only rarely do people who have sickle cell trait have complications similar to those seen in people who have sickle cell disease. But people who have sickle cell trait are carriers of a defective hemoglobin S gene, so they can pass it on when they have a child.
If the child’s other parent also has sickle cell trait or another abnormal hemoglobin gene, such as beta-thalassemia, hemoglobin C, hemoglobin D, or hemoglobin E, that child has a chance of having sickle cell disease.
In the image above, each parent has one normal hemoglobin A gene and one hemoglobin S gene, which means each of their children has:
It is important to keep in mind that each time this couple has a child, the chances of that child having sickle cell disease remain the same. In other words, if the firstborn child has sickle cell disease, there is still a 25% chance that the second child will also have the disease. Both boys and girls can inherit sickle cell trait, sickle cell disease, or normal hemoglobin.
If a person wants to know whether he or she carries a sickle hemoglobin gene, a doctor can order a blood test to find out.
In the United States, most people who have sickle cell disease are of African ancestry or identify themselves as Black.
There are also many people who have sickle cell disease who come from Hispanic, southern European, Middle Eastern, or Asian Indian backgrounds.
About 100,000 Americans have sickle cell disease.
People who do not know whether they carry an abnormal hemoglobin gene can ask their doctor to have their blood tested.
Couples who are planning to have children and know that they are at risk of having a child with sickle cell disease may want to meet with a genetic counselor. A genetic counselor can answer questions about the risk and explain the choices that are available.
If a person has sickle cell disease, it is present at birth. But most newborns do not have any problems from the disease until they are about 5 or 6 months of age.
The symptoms of sickle cell disease can vary from person to person and can change over time. Over time, you may experience symptoms depending on how sickle cell disease affects your health.
Early symptoms of sickle cell disease may include:
Complications of sickle cell disease include:
People who have sickle cell disease also usually have mild to moderate anemia. At times, however, they can have severe anemia. Severe anemia can be life-threatening. Severe anemia in a newborn or child who has sickle cell disease may be a result of:
Aplastic crisis and splenic sequestration crisis most commonly occur in newborns and children who have sickle cell disease. Adults who have sickle cell disease may also experience episodes of severe anemia, but these usually have other causes. Babies and newborns who have severe anemia may not want to eat and may seem very sluggish.
Your doctor may use a number of tests to diagnose sickle cell disease if various screening tests show that you might have the condition.
People who do not know whether they make sickle hemoglobin or another abnormal hemoglobin, such as SC, Sβ thalassemia, and SE, can find out by having their blood tested. This way, they can learn whether they carry a gene—or have the trait—for an abnormal hemoglobin that they could pass on to a child.
With this information, parents can be better informed about the chances of having a child with some type of sickle cell disease, such as hemoglobin SS or SC, Sβ thalassemia, or others.
When a child has sickle cell disease, early diagnosis is important to better prevent complications.
Every state in the United States, the District of Columbia, and the U.S. territories require that every baby be tested for sickle cell disease as part of a newborn screening program. In newborn screening programs, blood from a heel prick is collected in “spots” on a special paper. The hemoglobin from this blood is then analyzed in special labs. Newborn screening results are sent to the doctor who ordered the test and to the child’s primary doctor.
If a baby is found to have sickle cell disease, health providers from a special follow-up newborn screening group contact the family directly to make sure that the parents know the results. The child is always retested to be sure that the diagnosis is correct.
Newborn screening programs also find out whether the baby has an abnormal hemoglobin trait. If so, the parents are informed, and counseling is offered. Remember that when a child has sickle cell trait or sickle cell disease, a future sibling or the child’s own future child may be at risk.
Doctors can also diagnose sickle cell disease before a baby is born. This is done using a sample of amniotic fluid, the liquid in the sac surrounding a growing embryo, or of tissue taken from the placenta, the organ that attaches the umbilical cord to the mother’s womb.
Testing before birth can be done as early as 8 to 10 weeks into the pregnancy. This testing looks for the sickle hemoglobin gene rather than the abnormal hemoglobin.
A blood and bone marrow transplant is currently the only cure for some patients who have sickle cell disease. After early diagnosis, your doctor may recommend medicines or transfusions to manage complications, including chronic pain.
Babies who have sickle cell disease may see a hematologist, a doctor who specializes in blood diseases such as sickle cell disease. For newborns, the first sickle cell disease visit should take place before 8 weeks of age.
The U.S. Food and Drug Administration (FDA) approved a new medicine in 2019 to treat sickle cell disease in adults and children 12 years and older. The oral medicine prevents red blood cells from forming the sickle shape and binding together. This may decrease the destruction of some red blood cells, which in turn lowers the risk for anemia and improves blood flow to your organs.
Possible side effects include headache, diarrhea, abdominal pain, nausea, fatigue, and fever. Rarely, allergic reactions may occur, causing rashes, hives, or mild shortness of breath. Talk to your doctor about other medicines you take.
In 2019, the FDA also approved a new medicine to reduce the number of pain crises experienced by adults and children 16 years and older who have sickle cell disease. The medicine, which is given through an IV in the vein, helps prevent blood cells from sticking to blood vessel walls and causing blood flow blockage, inflammation, and pain crises.
Possible side effects include nausea, joint pain, back pain, and fever.
In children who have sickle cell disease, taking penicillin two times a day has been shown to reduce the chance of having a severe infection caused by the pneumococcus bacteria. Newborns need to take liquid penicillin. Older children can take tablets.
Many doctors will stop prescribing penicillin after a child has reached the age of 5. Some prefer to continue this antibiotic throughout life, particularly if a person has hemoglobin SS or hemoglobin Sβ0 thalassemia, since people who have sickle cell disease are still at risk. All people who have had surgical removal of the spleen, called a splenectomy, or a past infection with pneumococcus should keep taking penicillin throughout life.
Hydroxyurea is an oral medicine that has been shown to reduce or prevent several sickle cell disease complications.
Since hydroxyurea can decrease several complications of sickle cell disease, most experts recommend that children and adults with hemoglobin SS or Sβ0 thalassemia who have frequent painful episodes, recurrent chest crises, or severe anemia take hydroxyurea daily.
Hydroxyurea can cause the blood’s white cell count or platelet count to drop. Rarely, it can worsen anemia. These side effects usually go away quickly if a patient stops taking the medicine. When the patient restarts it, the doctor usually prescribes a lower dose.
It is still unclear whether hydroxyurea can cause problems later in life in people who have sickle cell disease and take the medicine for many years. Studies so far suggest that it does not put people at a higher risk of cancer and does not affect growth in children, but further studies are needed.
Your doctor may recommend transfusion to treat and prevent certain sickle cell disease complications. These transfusions may include:
A blood and bone marrow transplant is currently the only cure for sickle cell disease, but it is not for everyone. Most patients who have sickle cell disease either are too old for a transplant or do not have a relative who is a good enough genetic match to be a donor. A well-matched donor is needed for a patient to have the best chance for a successful transplant.
Most sickle cell disease transplants are currently performed in children who have had complications such as strokes, acute chest crises, and recurring pain crises. These transplants usually use a matched donor. Blood and bone marrow transplants are riskier in adults.
Several medical centers are looking into new ways to help more people who have sickle cell disease get a transplant. These include blood and bone marrow transplant techniques in children and adults who do not have a matched donor in the family or who are older than most recipients.
Blood and bone marrow transplants are successful in about 85% of children when the donor is related and HLA (human leukocyte antigen)-matched. Even with this high success rate, transplants still have risks. Complications can include severe infections, seizures, and other clinical problems. About 5% of people who have received such transplants have died. Sometimes transplanted cells attack the recipient’s organs. This is called graft-versus-host disease. You will get medicine to prevent many of the complications, but they still can happen.
Researchers at the NHLBI are exploring ways genetic therapies may help develop new treatments or find a cure for sickle cell disease. Genetic therapies aim to treat or cure conditions by adding new DNA or changing existing DNA.
Watch this video to learn about how genome editing works and how it could be used to treat sickle cell disease. Medical Animation Copyright © 2020 Nucleus Medical Media, All rights reserved.
Genetic therapy involves either restoring a faulty or missing gene or adding a new gene that improves the way the cell works. Researchers take blood or bone marrow from a patient and modify their stem cells in a laboratory using genetic therapies.
Genetic therapies that modify a person’s own hematopoietic stem cells may provide a cure for people who have sickle cell disease and do not have a well-matched donor. Modified stem cells can be injected into the blood, then the cells travel in the bloodstream to the marrow spaces inside the bones. Once inside the bone marrow, the cells can produce healthy red blood cells that do not sickle.
Follow these steps to help relieve symptoms and reduce your chances of serious problems, such as pain crises and other complications of sickle cell disease.
Prevent problems over your or your child’s lifetime
Sickle cell disease can lead to serious and life-threatening health problems. If you think you or someone else is having any of the following symptoms or complications, seek medical care or call 9–1–1 right away.
Pregnant women who have sickle cell disease are at greater risk for problems. If you are pregnant or planning for pregnancy, meet with a doctor who specializes in high-risk pregnancies and has experience with patients who have sickle cell disease.
Your doctor may prescribe certain vitamins and will be careful to prescribe pain medicines that are safe for you and your baby. You should not use hydroxyurea during pregnancy.
You may need to have one or more blood transfusions during pregnancy to treat problems, such as anemia symptoms that get worse. You may also experience more pain crises or be at higher risk of having acute chest syndrome. Your doctor will talk to you about how to help prevent these complications.
Learn about some of the ways we continue to translate current research into improved health for patients who have sickle cell disease. Research on this topic is part of the NHLBI’s broader commitment to advancing blood disorders and blood safety scientific discovery.
Learn about the pioneering research contributions we have made over the years that have improved clinical care and increased life expectancy for people who have sickle cell disease.
In support of our mission, we are committed to advancing sickle cell disease research in part through the following ways.
Learn about other exciting ways we are advancing research to improve the lives of people with sickle cell disease.
We lead or sponsor many studies on sickle cell disease. See whether you or someone you know is eligible to participate in our clinical trials.
To learn more about clinical trials at the NIH Clinical Center or to talk to someone about a study that might fit your needs, call the Office of Patient Recruitment 800-411-1222.
After reading our Sickle Cell Disease Health Topic, you may be interested in additional information found in the following resources.