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 hypotension, or high-output cardiac failure.

Important history to obtain when evaluating anemia includes the patient’s diet, prior blood counts, and prior episodes of jaundice. A family history of anemia, splenectomy, jaundice, or gallstones might suggest a hemoglobinopathy or a hereditary membrane disorder. Knowledge of any chronic disorders such as kidney disease, cardiovascular disease, or underlying inflammatory processes is necessary. Physical examination should assess for signs of jaundice, lymphadenopathy, or splenomegaly.

Laboratory evaluation of anemia should begin with a CBC, reticulocyte count, and review of the peripheral blood smear. Further diagnostic evaluation, if needed, is determined by the results of these tests unless specific historical elements or physical exam findings suggest a high probability diagnosis. Causes of anemia are most easily classified based on red blood cell (RBC) size (microcytic, normocytic, or macrocytic) and degree of bone marrow activity. The size of RBCs is measured as the mean corpuscular volume (MCV), the normal values of which vary with age. The lower limit of normal for the MCV equals 70 plus the age in years up to the normal adult low of 80. Bone marrow activity is reflected by the reticulocyte count. Table 104-1 summarizes the basic interpretation of a screening CBC for the cause for anemia. Table 104-2 reviews the interpretation of the peripheral smear examination of RBC morphology to help determine the cause of anemia.

The most common cause of microcytic anemia in children is iron deficiency. Thalassemia, anemia of inflammation, hemoglobin C disease, hemoglobin E disease, and sideroblastic anemia may also lead to microcytic anemia. Table 104-3 reviews a method for sorting out the common causes of microcytic anemia.