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Anemia may be the first recognized hematologic finding in a child
whose bone marrow is not functioning normally. It may be the sole
problem (single cytopenia) or occur in conjunction with deficits
in other cell lineages (pancytopenia). The cause may be a deficiency
of a required nutrient (iron, folic acid, vitamin B12),
the inability of the marrow to use nutrients because of concomitant
medical conditions (inflammation, hypothyroidism), or intrinsic
bone marrow failure. Bone marrow failure may be either inherited
or acquired (aplastic anemia). These anemias are due to diminished
RBC production.
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In pediatric patients, the most common nutritional anemia is
due to iron deficiency, which is discussed in Chapter 431. Anemias due to decreased production are generally macrocytic with
an increased mean cell volume (MCV) and mean cell hemoglobin (MCH).
Although diagnosed far more often in adults than children, most
commonly, nutritional anemias are due to a dietary deficiency of
folic acid, cobalamin (vitamin B12), or both.
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In both, the hemoglobin concentration is decreased, reticulocyte count
is inappropriately low for the degree of anemia, and mean cell volume
(MCV) and mean cell hemoglobin (MCH) are increased. The blood smear
shows macroovalocytes, anisocytosis, and poikilocytosis. Neutrophils
have hypersegmented nuclei. WBC and platelet counts are usually
within the normal range, but may decrease with more severe deficits. The
bone marrow shows ineffective erythropoiesis with erythroid hyperplasia
and delayed maturation of the nuclei compared to the cytoplasm.
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Folic acid deficiency is rare in infants and children in North
America due to the routine supplementation of commercial infant
formulas and flour-containing products such as bread and pasta.
Classically, it occurs with severe malnutrition and in infants fed
unpasteurized goat’s milk. As folic acid is absorbed in
the jejunum, malabsorption may occur with celiac disease or due
to the inhibitory effects of anticonvulsants such as Phenobarbital
and phenytoin. Cytotoxic medications, such as methotrexate, achieve
their therapeutic benefit by alteration of folic acid metabolism
(see Chapter 517). Deficiency may also occur
in persons with increased folate requirements such as in chronic hemolytic
anemia. Folic acid–deficient hematopoiesis is best diagnosed
by measurement of RBC, not serum, folate levels. Folate deficiency
is treated with oral medication.
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Cobalamin or
Vitamin B12 Deficiency
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This is also relatively uncommon in children, occurring most
often in breast-fed infants of mothers who are either strict vegetarians
or who themselves have pernicious anemia (due to antibodies against intrinsic
factor, which is required for absorption of vitamin B12). Absorption
of cobalamin occurs in the terminal ileum, so deficiency may develop
from impaired absorption that occurs in Crohn disease, pancreatitis,
bacterial overgrowth, and surgical resection of the terminal ileum.
Inborn errors of metabolism (transcobalamin II deficiency or methylmalonic
aciduria), and rarely lack of intrinsic factor, may also lead to
deficiency in childhood. Classically, ...