Abnormalities involving the blood may be divided into three groups:
* Anemia, a disorder in which there is an abnormally low level of hemoglobin or red cells in the blood and thus impaired delivery of oxygen to the tissues.
* Leukemia, a neoplastic blood disease characterized by an increase in the number of white cells.
* Clotting disorders. These disorders are characterized by an abnormal tendency to bleed due to a breakdown in the body’s clotting mechanism.
Anemia may result from loss of red cells, as through excessive bleeding (hemorrhage), or from conditions that cause the cells to hemolyze (rupture). In other cases, bone marrow failure or nutritional deficiences impede the production of red cells or hemoglobin.
Excessive Loss or Destruction of Red Cells Hemorrhagic loss of red cells may be sudden and acute or gradual and chronic. The average adult has about 5 liters of blood. If a person loses as much as 2 liters suddenly, death usually results. If the loss is gradual, however, over a period of weeks, or months, the body can compensate and withstand the loss of as much as 4 or 5 liters. Possible causes of chronic blood loss include bleeding ulcers, excessive menstrual flow, and bleeding hemorrhoids (piles). If the cause of the blood loss can be corrected, the body is usually able to restore the blood to normal. This process can take as long as 6 months, and until the blood returns to normal, the affected person may have anemia.
Hemolytic anemia Anemia caused by the excessive destruction of red cells is called hemolytic anemia. The spleen, along with the liver, normally destroys old red cells. Occasionally, an overactive spleen destroys the cells too rapidly, causing anemia. Infections may also cause red cell loss. For example, the malarial parasite multiplies in red cells and destroys them, and certain bacteria, particularly streptococci, produce a toxin that causes hemolysis. Certain inherited diseases that cause the production of abnormal hemoglobin may also result in hemolytic anemia. The hemoglobin in normal adult cells is of the A type and is designated HbA. In the inherited disease sickle cell anemia, the hemoglobin in many of the red cells is abnormal (HbS). When these cells give up their oxygen to the tissues, they are transformed from the normal disk shape into a sickle shape (Fig. 9-10). These sickle cells are fragile and tend to break easily. Because of their odd shape, they also tend to become tangled in masses that can block smaller blood vessels. When obstruction occurs, there may be severe joint swelling and pain, especially in the fingers and toes, as well as abdominal pain. This aspect of sickle cell anemia is referred to as sickle cell crisis. Sickle cell anemia occurs almost exclusively in black people. About 8% of African Americans have one of the genes for the abnormal hemoglobin and are said to have the sickle cell trait. It is only when the involved gene is transmitted from both parents that the clinical disease appears. About 1% of African Americans have two of these genes and thus have sickle cell disease. One drug has been found to reduce the frequency of painful crisis in certain adults. Hydroxyurea causes the body to make some hemoglobin of an alternate form (fetal hemoglobin) so that the red cells are not as susceptible to sickling. People taking hydroxyurea require blood tests every 2 weeks to assess for drug-induced bone marrow suppression.
Impaired Production of Red Cells or Hemoglobin
Many factors can interfere with normal red cell production. Anemia that results from a deficiency of some nutrient is referred to as nutritional anemia. These conditions may arise from a deficiency of the specific nutrient in the diet, from an inability to absorb the nutrient, or from drugs that interfere with the body’s use of the nutrient.
Figure 9-10 A blood smear in sickle cell anemia. Abnormal cells take on a crescent (sickle) shape when they give up oxygen.
Deficiency Anemia The most common nutritional anemia is iron-deficiency anemia. Iron is an essential constituent of hemoglobin. The average diet usually provides enough iron to meet the needs of the adult male, but this diet often is inadequate to meet the needs of growing children and women of childbearing age. A diet deficient in proteins or vitamins can also result in anemia. Folic acid, one of the B complex vitamins, is necessary for the production of blood cells. Folic acid deficiency anemia occurs in people with alcoholism, in elderly people on poor diets, and in infants or others suffering from intestinal disorders that interfere with the absorption of this water-soluble vitamin. Pernicious anemia is characterized by a deficiency of vitamin B12, a substance essential for proper red cell formation. The cause is a permanent deficiency of intrinsic factor, a gastric juice secretion that is responsible for vitamin B12 absorption from the intestine.
Neglected pernicious anemia can bring about deterioration in the nervous system, causing difficulty in walking, weakness and stiffness in the extremities, mental changes, and permanent damage to the spinal cord. Early treatment, including the intramuscular injection of vitamin B12 and attention to a prescribed diet, ensures an excellent outlook. This treatment must be kept up for the rest of the patient’s life to maintain good health.
Bone Marrow Suppression Bone marrow suppression or failure also leads to decreased red cell production. One type of bone marrow failure, aplastic anemia, may be caused by a variety of physical and chemical agents. Chemical substances that injure the bone marrow include certain prescribed drugs and toxic agents such as gold compounds, arsenic, and benzene. Physical agents that may injure the marrow include x-rays, atomic radiation,
radium, and radioactive phosphorus. The damaged bone marrow fails to produce either red or white cells, so that the anemia is accompanied by leukopenia, a drop in the number of white cells. Removal of the toxic agent, followed by blood transfusions until the marrow is able to resume its activity, may result in recovery. Bone marrow transplantations have also been successful. Bone marrow suppression also may develop in patients with certain chronic diseases, such as cancer, kidney or liver disorders, and rheumatoid arthritis. Some medications are now available to stimulate bone marrow production of specific types of blood cells. The hormone EPO made by recombinant methods (genetic engineering) can be given in cases of severe anemia to stimulate red cell production.
Leukemia is a neoplastic disease of blood-forming tissue. It is characterized by an enormous increase in the number of white cells. Although the cells are high in number, they are incompetent and cannot perform their normal jobs. They also crowd out the other blood cells. As noted earlier, the white cells have two main sources: red marrow, also called myeloid tissue, and lymphoid tissue. If this wild proliferation of white cells stems from cancer of the bone marrow, the condition is called myelogenous leukemia. When the cancer arises in the lymphoid tissue, so that most of the abnormal cells are lymphocytes, the condition is called lymphocytic leukemia. Both types of leukemia appear in acute and chronic forms. The cause of leukemia is unknown. Both inborn factors and various environmental agents have been implicated. Among the latter are chemicals (such as benzene), x-rays, radioactive substances, and viruses. Patients with leukemia exhibit the general symptoms of anemia because the white cells overwhelm the red cells. In addition, they have a tendency to bleed easily, owing to a lack of platelets. White cell failure lowers immunity, resulting in frequent infections. The spleen is greatly enlarged, and several other organs may be increased in size because of internal accumulation of white cells. Treatment consists of x-ray therapy and chemotherapy (drug treatment), but the disease is malignant and thus may be fatal. With new chemotherapeutic methods, the outlook is improving, and many patients survive for years.
A characteristic common to all clotting disorders is a disruption of the coagulation process, which brings about abnormal bleeding. Hemophilia is a rare hereditary bleeding disorder, a disease that influenced history by its occurrence in some Russian and Western European royal families. All forms of hemophilia are characterized by a deficiency of a specific clotting factor, most commonly factor VIII. In those with hemophilia, any cut or bruise may cause serious abnormal bleeding. The needed clotting factors are now available in purified concentrated form for treatment in cases of injury, preparation for surgery, or painful bleeding into the joints, a frequent occurrence in hemophilia. Cryoprecipitate contains factor VIII, and clotting factors are also produced by recombinant (genetic engineering) methods. Von Willebrand disease is another hereditary clotting disorder. It involves a shortage of von Willebrand factor, a plasma component that helps platelets to adhere (stick) to damaged tissue and also carries clotting factor VIII. This disorder is treated by administration of the appropriate clotting factor. In mild cases, a drug similar to the hormone ADH may work to prevent bleeding by raising the level of von Willebrand factor in the blood. The most common clotting disorder is a deficient number of circulating platelets (thrombocytes). The condition, called thrombocytopenia, results in hemorrhage in the skin or mucous membranes. The decrease in platelets may be due to their decreased production or increased destruction. There are several possible causes of thrombocytopenia, including diseases of the red bone marrow, liver disorders, and various drug toxicities. When a drug causes the disorder, its withdrawal leads to immediate recovery. Disseminated intravascular coagulation (DIC) is a serious clotting disorder involving excessive coagulation. This disease occurs in cases of tissue damage due to massive burns, trauma, certain acute infections, cancer, and some disorders of childbirth. During the progress of DIC, platelets and various clotting factors are used up faster than they can be produced, and serious hemorrhaging may result.