Sickle Cell Anemia and Trait

• Sickle cell anemia is an autosomal recessive disorder requiring inheritance of two genes.
• It results from structurally abnormal hemoglobin (hemoglobin S) in red blood cells.
• Hemoglobin S polymerizes under conditions of decreased oxygen, cold exposure, stress, and dehydration.
• Polymerization of hemoglobin S causes red blood cells to take on a sickle shape.
• Sickled red blood cells are rigid, vulnerable to destruction in the spleen, and cause anemia.

Sickle Cell Trait

• Sickle cell trait occurs when one allele for HbS is inherited from parents.
• Offspring with the sickle cell trait do not produce sickle cell anemia and are asymptomatic.
• Individuals with sickle cell trait can act as carriers and pass the faulty allele to their offspring.

Pathogenesis

• Hemoglobin S is formed due to hereditary substitution of valine for glutamine at the 6th position of the beta chain of hemoglobin.
• Hypercellularity of marrow occurs to compensate anemia which expands marrow cavities.
• Expansion of marrow cavities results in bossing of the skull, prominent malar bones, and protuberant teeth.
• Abnormal charge on the sickle cell surface increases adherence to endothelium, occluding vessels and impeding blood flow.
• Moderate splenomegaly, caused by congestion with sickled red cells, leads to spleen infarction.
• Repeated infarctions cause the spleen to become shrunken and fibrotic, a process known as "autosplenectomy".

Clinical Features

• Sickle cell disease typically manifests in the first year of life when fetal hemoglobin (HbF) levels decline.
• The decline in HbF leads to a switch from γ-globin to β-globin production.
• Manifestations of the switch from γ-globin to β-globin include fatigue, anemia, jaundice, and icterus (due to chronic hemolysis).
• Pigmented Gallstones can form due to increased bilirubin.
• Avascular necrosis of bones, particularly the femoral head, can occur.
• Sickle cell retinopathy may lead to blindness due to retinal detachment.
• Skull bossing results from compensatory bone marrow hyperplasia.

Acute Hemolytic Crises

• Hemolytic crises involve increased destruction of sickled red blood cells.
• Destruction of sickled red blood cells occurs both extravascularly (splenic sequestration) and intravascularly.
• Unlike aplastic crises, reticulocytes remain elevated during hemolytic crises.
• Aplastic crises involve a transient halt in erythropoiesis.
• Parvovirus B19 commonly causes aplastic crises which infects erythroid precursors.
• Infection of erythroid precursors by Parvovirus B19 leads to a drop in reticulocyte count and worsening anemia.
• Infarction crises are painful vaso-occlusive episodes caused by microvascular obstruction.
• Infarction crises commonly affect bones, spleen, and other organs.
• Infection, dehydration, and hypoxia precipitate infarction crises.

Investigations

• Complete Blood Count (CBC) may show low hemoglobin with a hematocrit volume of 20-30%.
• Reticulocyte count is typically high, around 10-25%.
• Sickled-shaped cells comprise 5-50% of red blood cells.
• White blood cells and platelets are elevated.
• Serum bilirubin level is high.
• Hemoglobin electrophoresis is used to find 85-98% hemoglobin S.
• There is no Hemoglobin A and a variable amount of hemoglobin F found with Hemoglobin electrophoresis.

Treatment

• Allogenic bone marrow transplantation is best for young patients with severe complications and an HLA-matched donor are best candidates for transplant.
• Hydroxyurea (cytotoxic drug) which increases the level of hemoglobin F.
• A dose of 500-750 mg/day of Hydroxyurea reduces the frequency of painful crises.
• Folic acid 5 mg daily supports the compensatory mechanism.
• Also include treatment and prevention of infections.
• Avoid dehydration and hypoxia (high altitude).
• NSAIDs or Opioid analgesics can treat pain. Blood transfusions

Nursing Management

• Administer opioids for severe pain and NSAIDs for mild pain.
• Apply warm compresses avoiding cold which can trigger sickling.
• Encourage oral fluids and IV hydration to reduce sickling and blood viscosity.
• Administer oxygen therapy only if hypoxia is present.
• Administer prophylactic antibiotics, such as penicillin, in children.
• Ensure up-to-date vaccinations, including pneumococcal, meningococcal, and Hib.
• Monitor for signs of infection, such as fever, malaise, and WBC count.
• Avoid extreme temperatures, dehydration, stress, and high altitudes.
• Monitor for the need for blood transfusions in severe cases of anemia.