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Anemia in infancy.

1. Jennifer Cobelli Kett, MD


 

1. Children’s National Medical Center Washington, DC

1. Anemia and Pallor . Kolb EA, Levy AS. In: McInerny TK, Adam HM, Campbell DE, Kamat DM, Kelleher KJ, eds. American Academy of Pediatrics Textbook of Pediatric Care. Elk Grove Village, IL: American Academy of Pediatrics; 2009:1395–1405.
 

2. Diseases of the Blood . In: Behrman RE, Kliegman RM, Jenson HB, eds. Nelson Textbook of Pediatrics. 17th ed. Philadelphia, PA: Saunders; 2004:1599–1678.
 

3. The Blood and Hematopoietic System . In: Martin RJ, Fanaroff AA, Walsh MC, eds. Fanaroff and Martin’s Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant. 8th ed. Philadelphia, PA: Mosby; 2006:1287–1356.
 

Anemia is the reduction in red blood cell (RBC) number, hematocrit, or hemoglobin concentration to a value >2 SDs below the age-specific mean. Anemia in infancy, which may result from increased erythrocyte loss or inadequate RBC production, raises unique considerations.

Understanding the development of the hematopoietic system may be helpful in the evaluation of neonates with anemia. Erythropoiesis begins in the yolk sac at 2 weeks’ gestation, generating cells that express embryonic hemoglobin. At 6 weeks’ gestation, the liver becomes the predominant site of RBC production, and the cells produced primarily express fetal hemoglobin. Not until 6 months’ gestation does the bone marrow become the major site of hematopoiesis. Throughout fetal life, erythrocytes decrease in size and increase in number: hematocrit increases from 30% to 40% during the second trimester to 50% to 63% at term. In late gestation and after birth, RBCs gradually switch from the production of fetal hemoglobin to adult hemoglobin.

After birth, RBC mass normally declines in response to an increase in the availability of oxygen and downregulation of erythropoietin. RBC count decreases until oxygen delivery is inadequate for metabolic demand and erythropoietin production is stimulated again. In healthy term infants, the RBC nadir, a physiologic response to postnatal life and not a hematologic disorder, typically occurs at 8 to 12 weeks of life and at a hemoglobin level of 9 to 11 g/dL.

Preterm infants also experience a decrease in hemoglobin concentration after birth, with a decline that typically is more abrupt and more profound than in term infants, reaching hemoglobin levels of …