Anemia, Sickle Cell

BASICS

Hereditary, hemoglobinopathy marked by chronic hemolytic anemia, acute episodes of painful crises, and increased susceptibility to infections
The heterozygous condition (Hb AS), sickle cell trait, is usually asymptomatic without anemia.
Synonym(s): sickle cell disease (SCD); Hb SS disease

~100,000 Americans have sickle cell anemia (SCA), and ~3 million people in the United States have sickle cell trait.
The condition affects mainly people of African descent. Hispanic, Middle Eastern, Asian Indian, and Mediterranean ancestry may also be affected.

Hemoglobin S (HbS) results from the substitution of the amino acid valine for glutamic acid at the sixth position of the β-globin chain.
HbS polymerization occurs in the RBC with increased concentrations of HbS and in deoxygenated states, resulting in RBC sickling.
Sickle RBCs exhibit increased adhesion, are inflexible, and have decreased ability to maneuver through small vessels leading to increased blood viscosity, stasis, and vaso-occlusion of small arterioles and capillaries, resulting in ischemia.
Sickle cell crises:
- Vaso-occlusive crisis: tissue ischemia and necrosis; progressive organ failure/tissue damage from repeated episodes
- Aplastic crisis: suppression of RBC production by severe infection (e.g., parvovirus and other viral infections)
- Hyperhemolytic crisis: accelerated hemolysis with reticulocytosis; increased RBC fragility/shortened lifespan
- Sequestration crisis: splenic sequestration of blood (only in young children as spleen is later lost to autoinfarction)
Hand–foot syndrome: Vessel occlusion/ischemia affects small blood vessels in hands or feet.

Autosomal recessive; homozygous condition, HbSS; heterozygous condition, HbAS
The heterozygous condition can also be combined with other hemoglobinopathies: Sickle cell hemoglobin C (HbSC) disease and Sβ + thalassemia are clinically similar to the heterozygous condition, whereas Sβ thalassemia is clinically similar to the homozygous condition.

Vaso-occlusive crisis: hypoxia, dehydration, high altitudes, stress, fever, infection, acidosis, cold, anesthesia, strenuous physical exercise, alcohol, smoking
Aplastic crisis: severe infections, human parvovirus B19 infection, folic acid deficiency
Hyperhemolytic crisis: acute bacterial infections, exposure to oxidant

Prevention of crises
- Avoid hypoxia, dehydration, cold, infection, fever, acidosis, and anesthesia.
- Prompt management of fever, infections, pain
- Avoid alcohol and smoking. Avoid high-altitude areas.
Minimizing trauma: Aseptic technique is imperative.

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