- The mean hemoglobin concentration for normal newborns is 18 g/dL, after which it falls to a nadir of 11.5 g/dL (mean concentration) at 2 to 3 months of life. Although mean hemoglobin concentrations in children continue to vary somewhat by age, 11 g/dL defines the lower limits of normal for the prepubertal patient population.
- Anemias are most easily classified based on red blood cell (RBC) size and degree of bone marrow activity. The size of RBCs is measured as mean corpuscular volume (MCV), with the lower limit of normal for the MCV equaling 70 plus the age in years; bone marrow activity is reflected by the reticulocyte count.
- The most common cause of microcytic anemia in childhood is iron deficiency, usually due to excess intake of whole cow's milk.
- Thalassemias are inherited defects resulting in the inability to synthesize sufficient quantities of various globin chains of the hemoglobin molecule. Thalassemia trait produces marked microcytosis out of proportion to the degree of anemia.
- If the reticulocyte count is high in the presence of a normocytic anemia, blood loss or a hemolytic process must be considered.
- A low reticulocyte count in the face of significant anemia indicates bone marrow underproduction. If the abnormality is isolated to the RBC line, the primary considerations are transient erythroblastopenia of childhood (TEC) or an aplastic crisis complicating an underlying hemolytic anemia.
- Thrombocytopenia or white blood cell (WBC) abnormalities associated with normocytic anemia and poor reticulocyte response suggests a marrow infiltrative process such as leukemia or acquired aplastic anemia.
- Macrocytic anemia is uncommon in pediatric patients. Folate and vitamin B12 deficiencies are rare in otherwise healthy children.
Physiologically, anemia occurs when the hemoglobin level is too low to meet cellular oxygen demands. Practically, anemia is defined as a hemoglobin concentration more than 2 standard deviations below the mean for a comparable population. The normal hemoglobin concentration varies by age and, in the postpubertal population, by sex. Hemoglobin values are high at birth and slowly fall to a nadir at 2 to 3 months of age. This nadir is deeper and occurs at a younger age in premature infants. Although mean hemoglobin concentrations in children continue to vary somewhat by age, 11 g/dL plus 0.1 times the age in years defines the lower limits of normal for the prepubertal patient population. After puberty, normative data for adult populations apply and gender differences become apparent.
Patients with mild anemia are usually asymptomatic, and the anemia is most commonly discovered on a routine complete blood count (CBC). Even children with moderate to severe anemia may be asymptomatic if the problem develops slowly, compensating well for even severely low hemoglobin levels. When the hemoglobin becomes low enough to produce symptoms, patients may present with fatigue, irritability, or shortness of breath on exertion. Physical examination may reveal pallor, tachycardia, jaundice, and systolic ejection murmur owing to an increased cardiac output. With a rapid drop in hemoglobin, the child may develop dizziness, orthostatic ...