Definition of Anemia
Anemia represents a decrease in red cell mass or hemoglobin content of blood below physiological need as set by tissue oxygen demand. The conventional limits for normal range of hemoglobin represent the values obtained for 95 per cent of a normal, healthy population, assuming a normal distribution of individuals (Table 1). In physiological terms, different ranges exist for men and women, for infants and growing children, and for different metabolic states. Anemia is an expression of many pathological conditions and is not itself a disease state but a clinical sign of such disorders. Therefore, analysis of any anemia should follow a tripartite logical pathway: (1) seek mechanisms by which the anemia occurs, e.g., bleeding, lack of red cell production, or excessive red cell destruction; (2) identify associated disease that cause anemia; (3) evaluate morphologically the peripheral blood smear (Figure 1).
Determinants of the normal range for hemoglobin, hematocrit, and red cell count include age, sex, and ambient altitude. Newborn infants have high values, which soon decline with rapid growth in infancy. Prepubertal boys and girls have similar values. At puberty, male sex hormones produce a rise in erythropoiesis so that adult males have hemoglobin levels approximately 2 to 4 gm/dl higher and hematocrits 5 to 7 percent higher than adult females. The healthy elderly normally suffer no decline in hemoglobin or hematocrit values; however, because of increased incidence of chronic disease, elderly populations may show slight decreases in these values. Populations living at altitudes over 4000 feet above sea level show increased hematocrits, which appear to represent physiological adaptation to the desaturation resulting from diminished atmospheric oxygen tension.
Table 1. Normal values for hemogram in adults
Figure 1. Photomicrographs of peripheral blood smears. Upper left, Spherocytes, round dense cells leaking a central pallor, in a patient with hereditary spherocytes. Upper right, Sickle cells, typicalof sickle cell anemia. Lower left, Target cells, typical of thalassemia. Lower right, Schistocytes, typical of microangiopathic hemolytic anemia.
Clinical Assessment of Anemia
Signs and symptoms of anemia vary with the rapidity of onset and with underlying disease of the cardiovascular dystem (Table 2). Thus, rapid blood loss, especially if plasma volume decreases rapidly, or brisk hemolysis may result in cardiovascular compensatory reactions, including tachycardia, postural hypotension, vasoconstriction in skin and extremities, dyspnea on exertion and faintness. Slowly developing anemias, such as those resulting from nutritional deficiency, permit gradual expansion of the plasma volume so that increased cardiac output gradually compensates. The subject may remain asymptomatic, noting only slight exertional dyspnea or in the case of pre-existing coronary artery disease, increased angina. Pallor of skin and mucous membranes, jaundice, cheilosis (fissuring of the angles of the mouth) a beefy red, smooth tongue, and koilonychia (spoon-shaped nails) are signs that accompany more advanced anemias of different types. The level of anemia at which signs of cardiovascular decompensation occur varies considerably with underlying disease, age, level of activity and the individual’s stoicism. For example, in the sedentary elderly person, a change in mentation can be an important clue to anemia, whereas decreased activity can mask exercise intolerance.
Evaluation of the anemic patient is best served by a systematic evaluation of the clinical and laboratory findings together (Figure 2). First, is the patient truly anemic? Increased plasma volume, fluid overload, or congestive heart failure may produce a dilutional anemia that disappears when fluid balance is restored. Second, is the anemia acquired or inherited? Family history is important, especially in hemolytic anemias, and a positive family history of jaundiase, splenomegaly, or gallstones may suggest such a condition.
Table 2. Clinical clues in evaluation of anemia
Figure 2. Laboratory screening for anemia
Dr. Afsaneh Jeddi