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Anemia is defined as reduced oxygen carrying capacity of the blood. Anemia can result from defective production, excessive destruction or blood loss.
Erythrocyte production requires the presence of bone marrow stem cells, erythropoietin, elemental iron, vitamins, cytokines and a suitable marrow micro environment. Underproduction of erythrocytes and resultant anemia results from abnormalities or disturbances of any of these key components. Iron deficiency anemia is most common in infants and young children with poor intake, but with malnutrition it is seen at any age. Infants who drink cow's milk as a sole source of nutrition are particularly susceptible to iron deficiency. Iron deficiency from malabsorption is rare but can occur in patients with celiac disease, chronic giardiasis and small bowel resections. Blood loss should always be considered, but it is more likely in older children and particularly in adolescent girls. Iron deficient children exhibit myriad behavioral and neurodevelopmental abnormalities, as iron is present not only in hemoglobin, but also in a number of important oxidative enzymes in the brain and other tissues. The diagnosis of iron deficiency is usually established by a trial of oral iron therapy. Elemental iron in a dose of 3-6 mg/kg/day in three divided doses will increase hemoglobin to safer levels in 2 to 3 weeks. The etiology of iron deficiency is usually apparent and measurements of serum iron, iron binding capacity and ferritin are not usually necessary. Iron treatment is usually continued for at least 3 months to correct the anemia. A further 3 to 6 months of replacement is necessary to replenish the iron stores. Failure of response should lead to the speculation about ongoing bleeding, patient compliance with iron therapy, poor absorption, or correctness of the diagnosis.
Thalassemia minor may mimic iron deficiency. The Mentzer index (MCV/RBC) may be helpful to differentiate Thalassemia minor from iron deficiency. In Iron deficiency, the index is generally> 13, where as in Thalassemia trait it is usually <13. Hepatosplenomegaly and more severe anemia is consistent with Thalassemia intermedia or Thalassemia major. Anemia of chronic disease can be associated with any severe infection or inflammatory disorder. The combination of low serum iron and iron binding capacity, with an elevated serum ferritin, are typical and help to differentiate it from iron deficiency anemia. Anemia is a late sign of lead poisoning and basophilic stippling is often present. Hereditary sideroblastic anemias are a rare group of disorders characterized by anemia, reticulocytopenia and abnormal patterns of iron deposition in marrow erythroblasts.
Pancytopenia with an impaired reticulocyte response warrants a bone marrow examination to rule out leukemia, marrow infiltration or aplastic anemia.
Anemia secondary to blood loss and hemolysis are much less common in children. Regardless of the etiology, the hemolytic anemias are characterized by accelerated destruction of red cells, which typically leads to indirect hyperbilirubinemia, increased urobilinogen excretion, and elevated lactate dehydrogenase. Bone marrow response leads to reticulocytosis. As intravascular hemolysis becomes more accelerated, free plasma hemoglobin and depressed serum haptoglobin levels may be detected. Chronic hemolysis leads to a detection of hemosiderin in the urine. Clinically, children present with symptoms of anemia, jaundice, splenomegaly, gallstones or peripheral non-healing ulcers.
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