The Difference Between Hemolytic And Sickle Cell Anemias

Hemolytic anemia refers to an anemia, a low red cell count or hemoglobin count, that is due to the excessive destruction of red cells. Lytic means destruction, in this case the destruction of red blood cells. There are many different hemolytic anemias, and this group includes sickle cell anemia. Hemolytic anemias are much less common than iron deficiency anemia, but are nonetheless important, largely because of the terrible effects of sickle-cell anemia.

The normal red blood cell lives between 90 to 120 days. New ones are constantly being made in our bone marrow, and the destruction of old cells and production of new ones is usually balanced so that anemia does not occur. If some process starts causing the destruction of red cells at a faster rate than usual, the bone marrow is able to raise its production of new cells by 6 to 8 times, assuming adequate iron and other essential elements are present. If the rate of destruction passes the ability of the marrow to compensate, then we see anemia developing. In many of the chronic hemolytic anemias, a new balance between destruction and production is found, and the resulting anemia may be only mild, unless some other factor such as infection temporarily slows production in the bone marrow, allowing the anemia to rapidly worsen.

The hemolytic anemias are usually categorized as hereditary, due to a genetic mutation that causes some aspect of the red cell to be abnormal, or acquired, meaning that something that causes normal red cells to be destroyed more rapidly has occurred. Sickle-cell anemia is probably the most common of the hereditary hemolytic anemias in the U.S., where it is found primarily in African Americans, but a type of inherited enzyme deficiency known as glucose-6-phosphate dehydrogenase (G6PD), is also fairly common, as is a generally mild condition called hereditary spherocytosis, in which the red cells are ball shaped spheres, instead of the normal hockey puck shape. In G6PD deficiency, found in African Americans and Mediterranean people, an acute hemolytic anemia may be precipitated by certain drugs, primarily those used to treat malaria, or by eating fava beans, which apparently contain a compound that stresses the deficient cells and leads to the hemolysis. People with G6PD deficiency will usually have no anemia at all until they are stressed by one of the compounds that causes the red cells to hemolyze, and in severe cases they can lose 25 percent of all their red cells in a brief period of time.

The spleen, and to some extent the liver, contain cells that specialize in removing old and deteriorated blood cells from the blood stream. The iron from the red cells is recirculated back to the bone marrow and is incorporated in the new cells formed there. Any condition which causes the spleen to enlarge may increase the number of cells removed, and normal as well as old cells may be hemolyzed. This is a condition called hypersplenism, and the white cells and platelets in the blood may be affected as well as the red cells. Conditions that may cause splenic enlargement and hypersplenism include leukemias, lymphomas, some inflammatory conditions, and cirrhosis of the liver. Removal of the spleen is usually advised if the destruction of any of the blood cells is significant.

In sickle-cell anemia, a particular mutation in the hemoglobin molecule causes the red blood cells to assume a sickle shape instead of the normal round hockey puck shape. These sickled cells are rapidly removed from the blood stream by the spleen and other organs, resulting in a chronic severe hemolytic anemia. The sickle cells can block the blood vessels in many organs including the lungs, kidneys, brain and bones. Sickle crises can occur, often brought on by infection, dehydration or reduced oxygen. People with sickle-cell anemia used to die before they grew into adulthood, but survival with modern treatment is much better and it is not unusual for people with few crises to live into their 50s. The hope that gene therapy would enable us to repair the hemoglobin mutation and cause the person to form normal red cells has unfortunately been difficult to achieve, but remains the goal for many doctors working in the area of sickle-cell disease.

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