Summary Points

• Most hemoglobinopathies are the result of single amino acid substitution in the beta chain.

• In sickle cell disorders, valine is substituted for glutamic acid in the sixth position of the beta chain.

• In hemoglobin C disorders, lysine is substituted for glutamic acid in the sixth position of the beta chain.

• The presence of hemoglobin S affords some protections against malarial infection of red blood cells.

• Cells containing hemoglobin S as the majority hemoglobin are insoluble in areas of the body with low oxygen tension.

• Sickle cells clog small vessels during sickling crisis, causing extensive organ damage and pain.

• Homozygous inheritance of hemoglobin S produces sickle cell anemia (Hgb SS); heterozygous inheritance produces sickle cell trait (Hgb AS).

• Hypoxia, acidosis, dehydration, cold, and fever will predispose the patient to sickling episodes.

• In the African American population, there is an 8% to 10% prevalence of the sickle cell gene.

Autosplenectomy is a consequence of repeated infarctions to the spleen in young children with sickle cell disease.

Stroke and acute chest syndrome represent serious complications to sickle cell patients. During sickle crisis episodes, patients will show nRBCs, sickle cells, target cells, and polychromasia. The white count may need to be corrected due to nRBCs present during sickling episodes. Individuals with sickle cell trait are asymptomatic with rare abnormalities in the peripheral smear. Newborn screening for hemoglobinopathies is available in the United States through state health laboratories.

Dithionite solubility is usually the screening procedure used to determine if hemoglobin S is present. Acid or alkaline electrophoresis and IEF provide better methods to isolate hemoglobin bands. Hemoglobin C disease occurs when hemoglobin C is inherited homozygously; hemoglobin C trait occurs when hemoglobin C is inherited heterozygously.

Hemoglobin C disease may produce hemoglobin C crystals on Wright's stain.

Hemoglobin SC is the result of inheriting two abnormal hemoglobins, hemoglobin S and C.

Hemoglobin SC may produce abnormal crystal formation resembling the Washington Monument or fingers in a glove presentation.

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