FIGURE 62.1 The diagnostic approach to pallor CBC, complete blood cell; WBC, white blood cell; PLT, platelet; RBC, red blood cell; MCV, mean corpuscular volume; G6PD, glucose-6phosphate dehydrogenase; DIC, disseminated intravascular coagulation; TEC, transient erythroblastopenia of childhood; HbSS, sickle cell anemia Numerous classifications of anemia have been used to assist the physician in the laboratory investigation of pallor Historically, the reticulocyte count and the MCV have been helpful measurements in categorizing causes of anemia The reticulocyte count can be performed rapidly and, as shown in Figure 62.1 , helps distinguish anemias caused by impaired red cell production (e.g., iron deficiency, hypoplastic anemia) from those caused by shortened red cell survival (e.g., hemoglobinopathies, membrane disorders, and other hemolytic states) The MCV provides a quick, accurate, and readily available method of distinguishing the microcytic anemias (iron deficiency, thalassemia syndromes) from the normocytic (membrane disorders, enzyme deficiencies, autoimmune hemolytic anemia, most hemoglobinopathies) or macrocytic (bone marrow/stem cell failure, disorders of B12 and folic acid absorption or metabolism) anemias The reticulocyte count and MCV should be interpreted with caution As shown in Figure 62.1 , disorders of shortened red cell survival are not always characterized by an increased reticulocyte count For example, reticulocytopenia may occur in autoimmune hemolytic anemia, despite active hemolysis and