Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Sickle cell anemia is an inherited blood disorder.

It causes:

  • Chronic destruction of red blood cells

  • Episodes of intense pain

  • Vulnerability to infections

  • Organ damage

  • In some cases, early death

Hemoglobin is a protein in red blood cells that carries oxygen. People with sickle cell anemia inherit a defective type of hemoglobin. When oxygen levels inside a red blood cell get low, the defective hemoglobin forms long rods. These rods stretch the red blood cells into long, abnormal "sickle" shapes. In contrast, normal red blood cells are disc-shaped.

Sickle-shaped red blood cells cannot easily pass through the body's blood vessels. Instead, they clog blood vessels. They block the flow of blood and cut off the oxygen supply to tissues and organs.

This lack of oxygen can damage the body's organs and limbs. It causes severe pain in any affected area.

A normal red cell's lifespan is 120 days. In contrast, sickled blood cells last only 10 to 20 days. As a result, patients with sickle cell disease have chronic anemia--an abnormally low level of red blood cells.

The spleen is an organ that helps clear infections. Sickle cell disease damages the spleen. By the time a child with sickle cell anemia is 4 years old, the spleen has usually stopped functioning. As a result, people with sickle cell disease have an increased risk of developing life-threatening infections.

To have fully developed sickle cell anemia, you must inherit one gene for the illness from each parent. Sometimes a person inherits only one sickle cell gene from one parent. This person is said to have sickle cell "trait" rather than sickle cell anemia. People with sickle cell trait usually have no symptoms. But, they can pass the gene to their children.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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