What Is Sickle Cell Anemia?

Sickle cell anemia is a serious condition in which the red blood cells can become sickle-shaped (that is, shaped like a “C”).

Normal red blood cells are smooth and round like a doughnut without a hole. They move easily through blood vessels to carry oxygen to all parts of the body. Sickle-shaped cells don’t move easily through blood. They’re stiff and sticky and tend to form clumps and get stuck in blood vessels.

The clumps of sickle cells block blood flow in the blood vessels that lead to the limbs and organs. Blocked blood vessels can cause pain, serious infections, and organ damage.

Normal and Sickled Red Blood Cells in Blood Vessels

Figure A shows normal red blood cells flowing freely in a blood vessel. The inset image shows a cross-section of a normal red blood cell with normal hemoglobin. Figure B shows abnormal, sickled red blood cells clumping and blocking the blood flow in a blood vessel. The inset image shows a cross-section of a sickled red blood cell with abnormal strands of hemoglobin.

Sickle cell anemia is an inherited, lifelong condition. People who have sickle cell anemia are born with it. They inherit two copies of the sickle cell gene, one from each parent. People who inherit a sickle cell gene from one parent and a normal gene from the other parent have a condition called sickle cell trait.

Sickle cell trait is different from sickle cell anemia. People with sickle cell trait don’t have the condition, but they have one of the genes that cause the condition. Like people with sickle cell anemia, people with sickle cell trait can pass the gene on when they have children. To learn more about sickle cell trait, see the section on causes of sickle cell anemia.

Anemia

Anemia (uh-NEE-me-uh) is a condition in which a person’s blood has a lower than normal number of red blood cells, or the red blood cells don’t have enough hemoglobin (HEE-muh-glow-bin). Hemoglobin is an iron-rich protein that gives blood its red color and carries oxygen from the lungs to the rest of the body.

Red blood cells are made in the spongy marrow inside the large bones of the body. Bone marrow constantly makes new red blood cells to replace old ones. Normal red blood cells last about 120 days in the bloodstream and then die. Their main role is to carry oxygen, but they also remove carbon dioxide (a waste product) from cells and carry it to the lungs to be exhaled.

In sickle cell anemia, a lower-than-normal number of red blood cells occurs because sickle cells don’t last very long. Sickle cells die faster than normal red blood cells, usually after only about 10 to 20 days. The bone marrow can’t make new red blood cells fast enough to replace the dying ones. The result is anemia.

Outlook

Sickle cell anemia affects millions of people worldwide. There are excellent treatments for the symptoms and complications of the condition, but in most cases there’s no cure. (Some researchers believe that bone marrow transplants may offer a cure in a small number of cases.)

Over the past 30 years, doctors have learned a great deal about the condition. They know what causes it, how it affects the body, and how to treat many of the complications. Today, with good health care, many people with the condition live close to normal lives and are in fairly good health much of the time. These people can live into their forties or fifties, or longer.

November 2007