Anemia, Sickle Cell
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- 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
- Sequestration crises and hand–foot syndrome seen typically in infants/young children
- Strokes occur mainly in childhood.
- Adolescence/young adulthood
- Frequency of complications and organ/tissue damage increases with age.
- Psychological complications: body image, interrupted schooling, restriction of activities; stigma of disease; low self-esteem
- Complicated, especially during 3rd trimester and delivery
- Fetal mortality 35–40%. Fetal survival is >90% if the fetus reaches the 3rd trimester.
- High prevalence of small for gestational age (SGA) babies
- Increased risk of thrombosis, preterm delivery, pain, toxemia, infection, pulmonary infarction, and phlebitis
- Partial exchange transfusion in 3rd trimester may reduce maternal morbidity and fetal mortality but is controversial.
- Chronic transfusions have been effective in diminishing pain episodes in pregnant women. However, this method should be used with caution due to risk of alloimmunization.
- ~90,000 Americans have sickle cell anemia (SCA), and 3.5 million people in the United States have sickle cell trait.
- The condition affects mainly people of African descent. Hispanic, Middle-eastern, and Asian Indian ancestry may also be affected.
Etiology and Pathophysiology
- Hemoglobin S results from the substitution of the amino acid valine for glutamic acid at the sixth position of the β-globin chain.
- HbS polymerizes in the RBC in the deoxygenated state resulting in RBC sickling.
- Sickle RBCs are inflexible, causes increased blood viscosity, stasis, obstruction of small arterioles and capillaries, and ischemia.
- Chronic anemia; crises
- Vaso-occlusive crisis: tissue ischemia and necrosis; progressive organ failure/tissue damage from repeated episodes
- Hand–foot syndrome: Vessel occlusion/ischemia affects small blood vessels in hands or feet.
- Aplastic crisis: suppression of RBC production by severe infection (e.g., parvoviral and other viral infections)
- Suppression of RBC production
- 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)
- Susceptibility to infection: impaired/absent splenic function leading to decreased ability to clear infection; defect in alternate pathway of complement activation
- Increased RBC destruction causes decreased hemoglobin levels and results in anemia and fatigue.
- Sickle cells exhibit increased adhesion and decreased ability to maneuver through small vessels, leading to vaso-occlusion.
- Autosomal recessive. Homozygous condition, Hb SS; heterozygous condition, Hb AS
- The heterozygote 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 (“painful crisis”): hypoxia, dehydration, fever, infection, acidosis, cold, anesthesia, strenuous physical exercise, smoking
- Aplastic crisis (suppression of RBC production): severe infections, human parvovirus B19 infection, folic acid deficiency
- Hyperhemolytic crisis (accelerated hemolysis with reticulocytosis): 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.