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Sickle cell disease (SCD) is an inherited hemolytic anemia that affects approximately 100,000 persons in the United States, mostly in the African-American population. It is responsible for lifelong medical complications in most affected individuals. Complications of SCD can be divided into those that are acute and those that are the result of the chronic repetitive vaso-occlusion of target organ systems (Table 89-1). This chapter focuses on the acute complications that the hospitalist is likely to encounter.
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SCD refers to a group of hemolytic anemias in which hemoglobin S (HbS) is present in either a homozygous state (HbSS) or in a compound heterozygous state, as when combined with hemoglobin C (HbSC) or hemoglobin beta-thalassemia (HbS-beta thalassemia). The HbS mutation is the result of an amino acid substitution (valine is substituted for glutamic acid at position 6) in the beta globin of the hemoglobin heterotetramer. The mutation creates a hydrophobic region that, in the deoxygenated state, facilitates a non-covalent polymerization of HbS molecules into rigid strands. These HbS polymers damage the erythrocyte membrane and change the rheology of the erythrocyte in circulation, causing erythrocyte dehydration hemolytic anemia and vaso-occlusion.
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CLINICAL PRESENTATION
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The National Institutes of Health recommends that all infants be screened in the neonatal period for SCD1 and all 50 states and the District of Columbia perform universal screening for SCD.2 For this reason, most children with SCD are identified early and medical management is started even before the usual age of presentation. Because the sickle mutation affects beta globin, a component of adult hemoglobin rather than fetal hemoglobin (HbF), affected infants are usually asymptomatic for the first 6 months of life. Anemia and complications from SCD usually present toward the end of the first year of life, after the physiologic switch from fetal to adult hemoglobin.
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Despite newborn screening and early identification, cases of previously undiagnosed SCD presenting with a medical complication do occur, and the clinician is advised to consider SCD in the differential of patients with non-immune hemolytic anemia. Although affected patients typically have moderate or severe anemia with hemoglobin values ranging from 7 to 9 g/dL, they generally are not overly symptomatic (e.g. weakness, fatigue) since the anemia ...