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  • Sickle cell syndromes, which can be divided into sickle cell trait (SCT) and sickle cell disease (SCD), are hereditary conditions characterized by the presence of sickle hemoglobin (HbS) in red blood cells (RBCs).

  • SCT is the heterozygous inheritance of one normal β-globin gene producing hemoglobin A (HbA) and one sickle gene producing HbS (HbAS) gene. Individuals with SCT are asymptomatic.

  • SCD can be of homozygous or compounded heterozygous inheritance. Homozygous HbS (HbSS) has historically been referred to as sickle cell anemia (SCA).


  • Clinical manifestations of SCD are due to impaired circulation, RBC destruction, and stasis of blood flow and ongoing inflammatory responses. These changes result from disturbances in RBC polymerization and to membrane damage. In addition to sickling, other factors contributing to the clinical manifestations include functional asplenia (and increased risk of bacterial infection), deficient opsonization, and coagulation abnormalities.

  • Polymerization allows deoxygenated hemoglobin to exist as a semisolid gel that protrudes into the cell membrane, distorting RBCs into sickle shapes. Sickle-shaped RBCs increase blood viscosity and encourage sludging in the capillaries and small vessels, leading to local tissue hypoxia that accentuates the pathologic process.

  • Repeated cycles of sickling, upon deoxygenation, and unsickling, upon oxygenation, damage the RBC membrane and cause irreversible sickling. Rigid, sickled RBCs are easily trapped, resulting in shortened circulatory survival and chronic hemolysis.


  • SCD involves multiple organ systems. Clinical manifestations depend on the genotype (Table 34–1).

  • Cardinal features of SCD are hemolytic anemia and vasoocclusion. Symptoms are delayed until 4 to 6 months of age when HbS replaces fetal hemoglobin (HbF). Common findings include pain with fever, pneumonia, splenomegaly, and, in infants, pain and swelling of the hands and feet (eg, hand-and-foot syndrome or dactylitis).

  • Usual clinical signs and symptoms of SCD include chronic anemia; fever; pallor; arthralgia; scleral icterus; abdominal pain; weakness; anorexia; fatigue; enlarged liver, spleen, and heart; and hematuria.

  • Acute complications of SCD include fever and infection (eg, sepsis caused by encapsulated pathogens such as Streptococcus pneumoniae), stroke, acute chest syndrome, and priapism. Acute chest syndrome is characterized by pulmonary infiltration, respiratory symptoms, and equivocal response to antibiotic therapy.

  • Acute episodes of pain can be precipitated by infection, dehydration, stresses, and sudden temperature changes. The most common type is vasoocclusive pain, which is manifested by pain over the involved areas without change in Hb. Aplastic crisis is characterized by acute decrease in Hb with decreased reticulocyte count manifested as fatigue, dyspnea, pallor, and tachycardia. Acute splenic sequestration is the sudden massive enlargement of the spleen due to sequestration of sickled RBCs. The trapping of sickled RBCs by the spleen leads to hypotension and shock, and can cause sudden death in young children. Repeated infarctions lead to autosplenectomy; therefore, incidence declines as adolescence approaches.

  • Chronic complications involve many organs and include pulmonary hypertension, bone and joint destruction, ocular problems, cholelithiasis, cardiovascular abnormalities, depression, ...

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