Anemia is defined as a hemoglobin concentration or hematocrit less than normal for a specific age and gender. Both age and gender are essential considerations when making a diagnosis of anemia, as is the fact that some laboratories use only adult normal range values and will erroneously report normal pediatric levels of hemoglobin as low. Using a definition of anemia as 2 standard deviations below the mean results in 2.5% of children meeting the criteria for anemia. Children with such “statistical anemia” should continue to follow along the same hembogloin percentile for age over time; but must also be confirmed as healthy and “normal” by ruling out other etiologies for anemia. Age-related normal means and ranges for hemoglobin, hematocrit, and mean corpuscular volume (MCV) are shown elsewhere (Table 425-1).
Normal erythrocytes circulate for 100 to 120 days, and at steady state, approximately 1% of old erythrocytes and 1% of new erthrocytes are released from the bone marrow into the circulation each day. Anemia results when there is an imbalance—congenital or acquired—in erythrocyte loss relative to production. Disorders resulting in decreased erythroid production are discussed in Chapter 428, and disorders that shorten the circulating erythrocyte lifespan are discussed in Chapters 429 and 430.
Erythrokinetic or Pathophysiologic
An erythrokinetic or pathophysiologic classification of anemia relies on the steady-state hemoglobin, reflecting a balance between marrow production of red blood cells (RBCs) and their rate of peripheral destruction. Thus, most anemias can be classified as disorders of either insufficient production or excessive loss from the circulation (eg, hemolysis, sequestration, bleeding). The primary laboratory indicator that distinguishes these disorders is the reticulocyte count. An appropriate increase in reticulocyte count in response to anemia suggests increased RBC losses. Conversely, an inappropriately “normal” or low reticulocyte count in response to anemia suggests a disorder of production.
Morphologic classification of anemia is based on the erythrocyte size as measured by the MCV and peripheral smear morphology. Most childhood anemias have a characteristic RBC appearance, which can either make or support the presumptive diagnosis (Fig. 426-1). A diagnostic algorithm that combines the pathophysiologic and morphologic criteria is shown in Figure 426-2.
Red blood cell morphology in various conditions.
Diagnostic algorithm for anemia. DAT, direct antiglobulin test; DIC, disseminated intravascular coagulation; G6PD, glucose-6-phosphate dehydrogenase; GI, gastrointestinal; HbS, hemoglobin S; HbC, hemoglobin C; HUS, hemolytic uremic syndrome; MCV, mean corpuscular volume; TEC, transient erythroblastopenia of childhood; TTP, thrombotic thrombocytopenic purpura.
The global anemia prevalence ...