Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Hemolytic Anemia

What Is It?

Anemia is an abnormally low level of red blood cells. Hemolytic anemia is the general name for any type of anemia that occurs because red blood cells are being destroyed too quickly.

Red blood cells are disc-shaped cells that contain hemoglobin and carry oxygen in the blood. Under normal circumstances, red blood cells are produced in the bone marrow and released into the bloodstream, where they circulate for 110 to 120 days. At the end of this period, the old red cells normally are removed from the blood by the spleen and liver.

In people with hemolytic anemia, red blood cells have an abnormally short life span. There are two major causes of this decrease in life span — either there is something wrong with the red blood cells or the red blood cells are normal but are destroyed by an external process.

Many different medical problems can cause hemolytic anemia, including:

• Inherited abnormalities in the cell membrane of red blood cells — In these genetic (inherited) illnesses, defects in proteins in the cell membrane (the outer coating of red blood cells) cause changes in the shape of the cells. Instead of being disc-shaped, the abnormal red cells form spheres, ellipses or tiny cups. These cells are more rigid than normal, and they become targets for the spleen, which identifies them as abnormal and removes them from circulation. These illnesses include hereditary spherocytosis, hereditary elliptocytosis, hereditary stomatocytosis and hereditary poikilocytosis.

• Inherited enzyme deficiencies inside red blood cells — Enzymes are proteins that drive the chemical reactions inside cells. When enzyme levels are abnormally low inside red blood cells, the cells become fragile and prone to being destroyed too quickly. The two most common inherited enzyme deficiencies that cause hemolytic anemia are pyruvate kinase deficiency and glucose-6-phosphate dehydrogenase (G6PD) deficiency.

• Hemoglobin disorders — In these illnesses, an inherited abnormality affects the hemoglobin inside red blood cells. Hemoglobin disorders include sickle cell anemia, other less common forms of hemoglobinopathy (an inherited illness in which hemoglobin has an abnormal structure), and the thalassemias (inherited illnesses that affecta red blood cell's ability to produce hemoglobin.)

• Physical damage to red blood cells — Hemolytic anemia can occur when red blood cells are damaged in any of the following situations: as they pass through machines that oxygenate blood outside the body during heart-lung surgery; as they flow near prostheses, especially artificial heart valves; or if they are exposed to extreme heat, as in a patient with severe, extensive burns.

• An autoimmune response — In this case, hemolytic anemia occurs because the body's immune system mistakenly destroys its own red blood cells. Autoimmune hemolytic anemia can be caused by other autoimmune conditions, such as systemic lupus erythematosus (SLE or lupus), by certain types of infections, such as hepatitis, and by medications, such as penicillin. In some cases, it has no clear cause.

• Hypersplenism — In this condition, an overactive, enlarged spleen traps circulating red blood cells and destroys them.