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Key Features

  • Hemoglobin C is formed by a single amino acid substitution at the same site as in sickle hemoglobin (codon 6 of the β globin gene) but with lysine instead of valine substituted for glutamine

  • Hemoglobin C is nonsickling but may participate in polymer formation in association with hemoglobin S

Clinical Findings

  • Homozygous hemoglobin C disease produces a mild hemolytic anemia with

    • Splenomegaly

    • Mild jaundice

    • Pigment (calcium bilirubinate) gallstones

  • Compared with patients who have homozygous SS disease, those with hemoglobin SC disease have

    • Milder hemolytic anemia

    • Milder clinical course

    • Fewer vaso-occlusive events

    • More retinopathy

    • More priapism

Diagnosis

  • Peripheral blood smear shows generalized red cell targeting and occasional cells with angular crystals of hemoglobin C

  • Persons heterozygous for hemoglobin C are clinically normal

  • Hemoglobin SC disease

    • Hematocrit is usually 30–38%, with 5–10% reticulocytes, and compared to SS, fewer irreversibly sickled cells on the blood smear

    • Target cells are more numerous than in SS disease

    • Hemoglobin electrophoresis shows approximately 45–50% hemoglobin C, 50% hemoglobin S, and no increase in hemoglobin F levels

Treatment

  • Folic acid 1 mg orally daily is advised; other treatment is usually necessary only for acute problems

  • Splenectomy is occasionally required

  • Cholecystectomy may be needed

  • Laser eye surgery if retinal neovascularization occurs

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