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General Considerations
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Anemia is defined as an abnormally low circulating red blood cell (RBC) mass, reflected by low serum hemoglobin (Hb). However, the normal range of Hb varies among different populations. For menstruating women, anemia is present if the Hb level is ≤11.6–12.3 g/dL. In men and postmenopausal women, anemia is present if the Hb level is ≤13.0-14.0 g/dL. Other factors, such as age, race, altitude, and exposure to tobacco smoke, can also alter Hb levels.
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Anemia is usually classified by cell size (Table 32-1). Microcytic anemias, mean corpuscular volume (MCV) < 80 fL, are usually due to iron deficiency, chronic inflammation, or thalassemia. Macrocytic anemias, MCV > 100 fL, are classified as megaloblastic or nonmegaloblastic. Megaloblasts are seen with vitamin B12 deficiency and folic acid deficiency. Nonmegaloblastic causes of macrocytosis include alcoholism, hypothyroidism, and chronic liver disease. Causes of normocytic anemia (MCV between 80 and 100 fL) are classified as either hemolytic or nonhemolytic.
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Normal Hb levels vary with age. At birth, mean Hb is ~16.5 g/dL. This level increases to 18.5 g/dL during the first week of life, followed by a drop to 11.5 g/dL by 1–2 months of age. This physiologic anemia of infancy is mediated by changes in erythropoietin levels. By 1–2 years of age, the Hb level begins to rise, to 14 g/dL in adolescent girls and 15 g/dL in adolescent boys. Thus, laboratory values in children should always be compared with age-appropriate norms.
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Many inherited causes of anemia are discovered in infancy and childhood. It is therefore important to obtain a careful family history in an anemic child, especially if the episodes of anemia are intermittent. Sickle cell anemia, thalassemia, glucose-6-phosphate dehydrogenase (G6PD) deficiency, and spherocytosis are examples of inherited forms of anemia.
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Other elements of the history are also important when evaluating a child for anemia. Because infants with anemia can exhibit poor feeding, irritability, and tachycardia rather than classic adult symptoms and signs, these atypical features should be explored with the family. Nutrition should be evaluated carefully, with attention to dietary sources of vitamin B12...