Anemia Introduction
Anemia is a blood disorder characterized by the reduction in:
Table of Contents
- Red blood cell count
- Hemoglobin content
- Packed cell volume.
Generally, reduction in RBC count, hemoglobin content, and PCV occurs because of:
- Decreased production of RBC
- Increased destruction of RBC or
- Excess loss of blood from the body
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All these incidents are caused either by inherited disorders or environmental influences such as nutritional problems, infection, and exposure to drugs or toxins.
Classification Of Anemia
Anemia is classified by two methods
- Morphological classification
- Etiological classification.
1. Morphological Classification
- The morphological classification depends upon the size and color of the RBC. The size of RBC is determined by mean corpuscular volume (MCV).
- Color is determined by mean corpuscular hemoglobin concentration (MCHC). By this method, the anemia is classified into four types:
- Normocytic Normochromic Anemia: The size (MCV) and color (MCHC) of RBCs are normal. But the number of RBCs is less.
- Macrocytic Normochromic Anemia: The RBCs are larger in size with normal color. The RBC count is less.
- Macrocytic Hypochromic Anemia: The RBCs are larger in size MCHC is less so the cells are pale (less colored).
- Microcytic Hypochromic Anemia: The RBCs are smaller in with less color.
2. Etiological Classification: On the basis of the etiology (study of cause or origin), the anemia is divided into five types:
- Hemorrhagic anemia
- Hemolytic anemia
- Nutrition deficiency anemia
- Aplastic anemia
- Anemia of chronic disease.
- Hemorrhagic Anemia: Hemorrhage refers to excessive loss of blood. Anemia due to hemorrhage is known as hemorrhagic anemia. It occurs both in acute and chronic hemorrhagic conditions.
- Acute hemorrhage:
- It refers to sudden loss of a large quantity of blood as in the case of an accident. Within about 24 hours after the hemorrhage, the plasma portion of blood is replaced.
- However, the replacement of RBCs does not occur quickly and it takes at least 4-6 weeks. So with less number of RBCs, hemodilution occurs. However, morphologically the RBCs are normocytic and normochromic.
- A decreased RBC count causes hypoxia which stimulates the bone marrow to produce more number of RBC. So, the condition is corrected within 4-6 weeks.
- Chronic hemorrhage
- It refers to the loss of blood by internal or external bleeding over a long period of time. It occurs in conditions like peptic ulcer, purpura, hemophilia, and menorrhagia.
- Due to the continuous loss of blood, a lot of iron is lost from the body causing iron deficiency. This affects the synthesis of hemoglobin resulting in less hemoglobin content in the cells. The cells also become small. Hence, the RBCs are microcytic and hypochromic
- Acute hemorrhage:
- Hemolytic Anemia: Hemolysis means the destruction of RBCs. Anemia due to excessive hemolysis which is not compensated by increased RBC production is called hemolytic anemia It is classified into two types:
- Extrinsic hemolytic anemia
- Intrinsic hemolytic anemia
- Extrinsic hemolytic anemia: It is the type of anemia caused by the destruction of RBCs by external factors. The healthy RBCs are hemolyzed by factors outside the blood cells such as antibodies, chemicals, and drugs. Extrinsic hemolytic anemia is also called autoimmune hemolytic anemia. The common causes of external hemolytic anemia are:
- Liver failure
- Renal disorder
- Hypersplenism
- Burns
- Infections like hepatitis, malaria, and septicemia
- Drugs such as penicillin, antimalarial drugs, and sulfą drugs
- Poisoning by chemical substances like lead, coal, and tar
- The presence of isoagglutinin-like anti-Rh
- Autoimmune diseases such as rheumatoid arthritis and ulcerative colitis.
- Intrinsic hemolytic anemia: it is the type of anemia caused by the destruction of RBCs because of defective S&Cs.
- There is production of unhealthy RBCs which are short-lived and destroyed soon. Intrinsic hemolytic anemia is often inherited and it includes sickle cell anemia and thalassemia.
- Because of the abnormal shape in sickle cell anemia and thalassemia, the RBCs become more fragile and susceptible for hemolysis.
- Sickle cell anemia
- Sickle cell anemia is an inherited blood disorder characterized by sickle-shaped red blood cells. It is also called hemoglobin SS disease or sickle cell disease. It is common in people of African origin.
- Sickle cell anemia is due to abnormal hemoglobin called hemoglobin S (sickle cell hemoglobin). In this, chains are normal and ẞ chains are abnormal.
- The molecules of hemoglobin S polymerize into long chains and precipitate inside the cells. Because of this, RBCs attain a sickle (crescent) shape and become more fragile leading to hemolysis.
- Sickle cell anemia occurs when a person inherits two abnormal genes (one from each parent).
- In children, hemolyzed sickle cells aggregate and block the blood vessels leading to infarction (stoppage of blood supply). The infarction is common in small bones.
- The infarcted small bones in the hand and foot results in varying lengths in the digits. This condition is known as hand and foot syndrome. Jaundice also occurs in these children.
- Thalassemia: Thalassemia is a group of inherited disorders characterized by abnormal hemoglobin. It is also known as Cooley’s anemia or Mediterranean anemia. It is more common in Thailand and to some extent in Mediterranean countries. Thalassemia is of two types:
- α thalassemia
- ẞ thalassemia.
- The ẞ thalassemia is very common among these two. In normal hemoglobin, the number of a and ẞ polypeptide chains is equal.
- In thalassemia, the production of these chains becomes imbalanced because of defective synthesis of globin genes.
- This causes the precipitation of the polypeptide chains in the immature RBCs leading to disturbance in erythropoiesis. The precipitation also occurs in mature red cells resulting in hemolysis.
- α Thalassemia: The α thalassemia occurs in fetal life or infancy. In this a chains are less, absent, or abnormal. In adults ẞ chains are in excess and in children γ chains are in excess. This leads to defective erythropoiesis and hemolysis. The infants may be stillborn or may die immediately after birth.
- ẞ Thalassemia: In ẞ thalassemia ẞ chains are less in number, absent, or abnormal with an excess of α chains. The α chains precipitate causing defective erythropoiesis and hemolysis.
- Extrinsic hemolytic anemia: It is the type of anemia caused by the destruction of RBCs by external factors. The healthy RBCs are hemolyzed by factors outside the blood cells such as antibodies, chemicals, and drugs. Extrinsic hemolytic anemia is also called autoimmune hemolytic anemia. The common causes of external hemolytic anemia are:
- Nutrition Deficiency Anemia; Anemia that occurs due to a deficiency of a nutritive stance necessary for erythropoiesis is called nutrition deficiency anemia. The substances that are necessary for erythropoiesis are iron, proteins, and vitamins like C, B12, and folic acid. The types of nutrition deficiency anemia are:
- Iron deficiency anemia: Iron deficiency anemia is the most common type of anemia. It develops due to the inadequate availability of iron for hemoglobin synthesis. The RBCs are microcytic and hypochromic. The causes of iron deficiency anemia are:
- Loss of blood
- Decreased intake of iron
- Poor absorption of iron from the intestine
- Increased demand for iron in conditions like growth and pregnancy.
- The features of iron deficiency anemia are brittle nails, spoon-shaped nails (koilonychia), brittle hair, atrophy of papilla in the tongue, and dysphagia (difficulty in swallowing).
- Protein deficiency anemia: Due to a deficiency of proteins, the synthesis of hemoglobin is reduced. The RBCs are macrocytic and hypo-chromic.
- Pernicious anemia or Addison’s anemia
- It is the anemia due to a deficiency of vitamin B12, It is also called Addison’s anemia. It is due to atrophy of the gastric mucosa because of autoimmune destruction of parietal cells.
- Gastric atrophy results in decreased production of intrinsic factors and poor absorption of vitamin B12 which is the maturation factor for RBC. The RBCs are larger and immature with almost normal or slightly low hemoglobin levels.
- The synthesis of hemoglobin is almost normal in this type of anemia. So, cells are macrocytic and normochromic/hypochromic.
- Before knowing the cause of this anemia, it was very difficult to treat the patients, and the disease was considered to be fatal. So, it was called pernicious anemia.
- Pernicious anemia is common in old age and it is more common in females than in males. It is associated with other autoimmune diseases like disorders of the thyroid gland, Addison’s disease, etc.
- The characteristic features of this type of anemia are a lemon yellow color of skin (due to anemic paleness and mild jaundice), and a red sore tongue.
- Neurological disorders such as paresthesia (abnormal sensations like numbness, tingling, burning, etc.), progressive weakness, and ataxia (muscular incoordination) are also observed in extreme conditions.
- Megaloblastic anemia
- Megaloblastic anemia is due to the deficiency of another maturation factor called folic acid. Here the RBCs are not matured. The DNA synthesis is also defective so the nucleus remains immature. The RBCs are megaloblastic and hypochromic.
- The features of pernicious anemia appear in megalo-blastic anemia also. However, neurological disorders may not develop.
- Iron deficiency anemia: Iron deficiency anemia is the most common type of anemia. It develops due to the inadequate availability of iron for hemoglobin synthesis. The RBCs are microcytic and hypochromic. The causes of iron deficiency anemia are:
- Aplastic Anemia; Aplastic anemia is due to the disorder of the red bone marrow. The red bone marrow is reduced and replaced by fatty tissues. Bone marrow disorder occurs in the following conditions:
- Repeated exposure to X-ray or gamma-ray radiation
- Presence of bacterial toxins, quinine, gold salts, benzene, radium, etc.
- Tuberculosis
- Viral infections like hepatitis and HIV infections. In aplastic anemia, the RBCs are normocytic and normochromic.
- Anemia of Chronic Diseases
- Anemia of chronic diseases is the second most common type of anemia (next to iron deficiency anemia). It is characterized by the short life span of RBCs caused by a disturbance in iron metabolism or resistance to erythropoietin action.
- Anemia develops after a few months of sustained disease. The RBCs are normocytic and normochromic. Common causes of this type of anemia are:
- Noninfectious inflammatory diseases such as rheumatoid arthritis (chronic inflammatory auto-immune disorder affecting joints)
- Chronic infections like tuberculosis (infection caused by Mycobacterium tuberculosis) and abscesses (collection of pus in the infected tissue) in the lungs
- Chronic renal failure in which the erythropoietin secretion decreases (since erythropoietin is necessary for the stimulation of bone marrow to produce RBCs, its deficiency causes anemia)
- Neoplastic disorders (abnormal and disorganized growth in tissue or organ) such as Hodgkin’s disease (malignancy involving lymphocytes) and cancer of the lung and breast.
The red cells are generally normocytic and normochromic in this type of anemia. However, in progressive disease associated with iron deficiency, the cells become microcytic and hypochromic.
Signs And Symptoms Of Anemia
- Skin:
- The color of the skin becomes pale. The paleness is more constant and prominent in the buccal and pharyngeal mucous membrane, conjunctivae, lips, ear lobes, palm, and nail bed.
- Skin becomes thin and dry losing elasticity. Thinning, loss, and early grayness of hair occur. The nails become brittle and easily breakable.
- Cardiovascular System: There is an increase in heart rate (tachycardia) and cardiac output. The heart is dilated and cardiac murmurs are produced. The velocity of blood flow is increased.
- Respiration: There is an increase in the rate and force of respiration. Sometimes, it leads to breathlessness and dyspnea (difficulty in breathing). The oxygen hemoglobin dissociation curve is shifted to the right.
- Digestion: Anorexia, nausea, vomiting, abdominal discomfort, and constipation are common. In pernicious anemia, there is atrophy of papillae in the tongue. In aplastic anemia, necrotic lesions appear in the mouth and pharynx.
- Metabolism: Basal metabolic rate increases in severe anemia.
- Kidney: Renal function is disturbed. Albuminuria is common.
- Reproductive System: In females, the menstrual cycle is disturbed. There may be menorrhagia, oligomenorrhea, or amenorrhea.
- Neuromuscular System: The common neuromuscular symptoms are headaches, lack of concentration, restlessness, irritability, drowsiness, dizziness, or vertigo especially when standing, and increased sensitivity to cold and fainting sensations. Muscles become weak and the patient feels a lack of energy and fatigued quite often and quite easily.
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