extended hyperalimentation, intestinal resection, or chronic diarrhea Affected infants usually present with failure to thrive and developmental delay Older patients more commonly exhibit weight loss, constipation, and weakness The diagnosis of vitamin B12 or folic acid deficiency may be suggested by the finding of anemia with megaloblastic features Megaloblastic anemia is characterized by normochromic, macrocytic red blood cells, hypersegmented neutrophils, and an elevated serum level of lactic dehydrogenase The diagnosis is confirmed by the finding of low serum levels of folic acid or vitamin B12 and the response to folic acid or vitamin B12 replacement therapy TABLE 62.1 PALLOR WITHOUT ANEMIA Physiologic (“fair-skinned”) Shock: septic, hypovolemic, neurogenic, cardiogenic, anaphylactoid Hypoglycemia and other metabolic derangements Respiratory distress Skin edema Pheochromocytoma Hypoplastic and Aplastic Anemias Pallor is usually the first sign of aplastic or hypoplastic anemia These anemias may be congenital or acquired Congenital aplastic anemias are most commonly part of larger syndromes The two major recognized syndromes are Diamond– Blackfan and Fanconi anemia Diamond–Blackfan syndrome is a congenital hypoplastic anemia commonly detected in the first few months of life The anemia can be severe at the time of diagnosis The red cells are normocytic or macrocytic The reticulocyte count is characteristically low Associated congenital anomalies include microcephaly, cleft palate, web neck, and thumb irregularities The diagnosis is made by examination of a bone marrow aspirate evidencing markedly reduced or absent erythrocyte precursors with normal marrow cellularity