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HEMATOLOGIC EMERGENCIES
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DISORDERS OF RED BLOOD CELLS
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Hemoglobin (Hb) and hematocrit for a child will vary depending on the age of the child, which is of key importance in the diagnosis of anemia. Table 40–1 lists average Hb values by age. In the neonatal period, Hb levels are elevated due to polycythemia of the fetus, with average Hb of 17 mg/dL at birth. Equilibration occurs over the first 2 months, leading to a physiologic nadir of about 11 mg/dL at 2 months of age. Hb levels normalize by approximately 6 months of age and remain so until adolescence, with an average level of 12-13 mg/dL. In adolescence, Hb levels diverge between boys and girls due to differences in hormones and onset of menses in girls.
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Severe anemia may be due to acute or chronic disorders. The child with acute blood loss leading to anemia may present with signs of hypovolemic shock, including tachycardia, delayed capillary refill, cool extremities, mental status changes, respiratory distress, and in advanced cases, hypotension. However, children generally tolerate severe anemia from a chronic cause and may remain asymptomatic to Hb levels of 5-6 g/dL. Chronic severe anemia is most commonly due to iron deficiency, but can also be due to deficiencies of folate, vitamin B12, copper or vitamin E, or to inherited hemoglobinopathies. Presentation may include symptoms of lethargy, fatigue or poor feeding, and physical findings of pallor, mild tachycardia, and systolic murmur, without signs of hypovolemic shock. Children should be carefully examined for signs of heart failure, including hepatomegaly and cardiomegaly. Iron deficiency is most commonly due to nutritional deficiency in children younger than 3 years; older children require gastrointestinal evaluation to identify sources of possible occult blood loss. Possible causes of anemia can be identified by measurement of the mean corpuscular volume (MCV) on the complete blood cell count (CBC). Table 40–2 outlines causes of anemia based on low, normal, and high MCV.
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