Disorders of Erythrocytes

Disorders of Erythrocytes

The majority of erythrocyte disorders are classified as either anemia or polycythemia. There are a variety of anemias, and fewer varieties of polycythemias.

Anemias

The term anemia signifies the blood having an ability to carry oxygen that is too low for normal metabo-lism. This is not an actual disease, but a sign of some type of disorder. When a person is anemic, he or she is chilled, fatigued, short of breath, and often pale. The three causes of anemia include blood loss, insufficient production of red blood cells, or excessive destruction of red blood cells.

Blood Loss

Blood loss causes hemorrhagic anemia. When this condition is acute, blood loss is very rapid, and is treated by replacing this depleted blood. Chronic hemorrhagic anemia may be caused by small amounts of blood being lost, but on a persistent basis, such as from a bleeding ulcer or because of hemorrhoids. After the primary condition is resolved, lost blood cells can be replaced by normal erythropoiesis. After losing a fair amount of blood, there would be an increased reticulocyte count.

Insufficient Production of Red Blood Cells

There are a variety of causes that result in insufficient production of RBCs, including total failure of red bone marrow function, and lack of essential raw mate-rials such as iron.

■■ Aplastic anemia—red bone marrow destructionor inhibition because of chemicals, drugs, ioniz-ing radiation, viruses, or most commonly from an unknown cause. Since all formed elements expe-rience altered development, anemia is usually present along with defective blood clotting and immunity. Blood transfusions may be beneficial until stem cells can be harvested from a donor’s blood or bone marrow, or if umbilical cord blood can be transplanted.

■■ Pernicious anemia—an autoimmune diseasethat is most common in the elderly, in which the stomach mucosa is destroyed by their own immune systems. In order for intestinal cells to absorb vitamin B₁₂ require intrinsic factor, which is produced by the mucosal cells of the stomach. Developing erythrocytes can grow but not divide without vitamin B₁₂. This causes large, pale cells to develop, which are known as macro-cytes. Treatment of pernicious anemia requiresregular intramuscular vitamin B₁₂ injections, or a nasal application of a gel containing this vitamin, once weekly. Also, a lack of dietary vitamin B₁₂ can cause anemia, but this usually only occurs in strict vegetarians, since this vitamin is found in large amounts in fish, poultry, and other meats.

■■ Iron-deficiency anemia—this form of anemiausually follows hemorrhagic anemia, but may also occur because of inadequate dietary iron or impaired absorption of iron. Microcytes are pro-duced, which are a type of erythrocytes that are small and pale, due to their inability of ­synthesizing normal amounts of hemoglobin. Iron-­deficiency anemia is treated by increasing dietary iron or by taking iron supplements.

■■ Renal anemia—this form of anemia is causedby lack of erythropoietin (EPO), which controls ­production of red blood cells. It often occurs because of renal disease, in which the kidneys cannot produce enough EPO. Treatment involves the administration of synthetic EPO.

Excessive Destruction of Red Blood Cells

Hemolytic anemias involve premature rupture or lysisof erythrocytes. Causes include abnormal hemo-globin, certain bacterial or parasitic infections, and transfusions of mismatched blood. When abnormal hemoglobin is produced, there is usually a genetic cause. The two primary examples are thalassemias and sickle-cell anemia, which are serious disorders that may be incurable and fatal. These diseases involve abnormal globin and erythrocytes that are fragile, which rupture prematurely.

■■ Thalassemias — most common in people of Mediterranean ancestry, these conditions involve one globin chain that is absent or has abnormal function. Erythrocytes have less hemoglobin than normal, and appear thin and delicate. A large variety of thalassemias occur, which are classified by their hemoglobin chains that are affected, and where in the chains that this occurs. Some are mild, while others are so severe that they require monthly blood transfusions.

■■ Sickle cell anemia— because of a change in one of the 146 amino acids of a beta chain in the globin molecule, abnormal hemoglobin S (HbS) is formed. When low-oxygen conditions exist, the beta chains link together, forming stiff rods. The hemoglobin S becomes sharp and has “spikes.” This causes RBCs to adopt a crescent shape when they deliver molecules of oxygen, or when oxygen content of the blood is low, such as during vigorous exercise. The deformed erythrocytes easily rupture and often block small blood vessels. This interferes with delivery of oxygen, causing severe bone and chest pain, other severe pain, and impaired breathing. Infections and stroke often result. For acute sickle-cell crisis,blood transfusions are still performed regularly.A newer treatment involves inhalation of nitric oxide to dilate the blood vessels. Sickle cell anemia mostly affects Africans living in areas of that country where malaria occurs regularly, and their descendants. Nearly one of every 00 African­ -American babies has this disease.

Individuals with two copies of the sickle cell gene have sickle-cell anemia, but those with only one copy of the gene have sickle-cell trait, and are more likely to survive malaria. The cells only sickle when the individual is infected with malaria, or under other abnormal situations. The sickling reduces likelihood of the malaria para-sites’ survival. It also increases the ability of mac-rophages to destroy infected RBCs and parasites inside them. Treatments focus on preventing RBCs from sickling. For example, fetal hemoglo-bin (HbF) does not sickle, even in people likely to develop sickle-cell anemia. Therefore, hydroxy-urea can be administered, since it causes the fetal hemoglobin gene to activate. This greatly relievespain and severity of sickle-cell complications, by 50%. In children with severe disease, bone marrow stem cell transplants are risky but may be totally curative. Newer treatments include orally -administered arginine, which stimulates nitric oxide production and dilates blood vessels, as well as gene therapy.

Polycythemias

Polycythemia results in the blood to become slug-gish, due to excessive amounts of erythrocytes, and elevated hematocrit. A bone marrow cancer called polycythemia vera results in an extremely high RBCcount, of 8 to 11 million cells per microliter, and also causes dizziness. Blood volume may be doubled, severely impairing circulation, and the hematocrit may be as high as 80%. Treatment for severe cases involves therapeutic phlebotomy , in which some blood is removed from the body. Secondary polycy-themias involve low oxygen or increased erythropoi-etin. In people living at high altitudes, it may occur as a normal response to reduced atmospheric pres-sure and resultant lower oxygen content in the air. In these individuals, the RBC count is often between 6 and 8 million per microliter.

Artificially induced polycythemia, or blood dop-ing, is often done by athletes who compete in aerobicevents. The RBCs are partially drawn off and stored. The body replaces them quickly. A few days before the athletic competition, the stored blood is reinfused, causing a temporary polycythemia. Theoretically, this should cause increased oxygen-carrying because of higher hematocrit, and greater speed and endurance. This does occur, but risks include potential stroke and heart failure. The practice has been labeled “unethi-cal,” and has since been banned from competitions such as the Olympics.