Sickle cell trait (Hb AS) is a benign carrier condition, usually with none of the symptoms of sickle cell anemia. It is generally only a laboratory diagnosis in which one sickle cell beta-globin gene has been inherited along with a normal beta-globin gene (ie, alpha2/betaS1beta1).
The diagnosis, differential diagnosis, and complications of sickle cell trait will be discussed here. Homozygous sickle cell disease and the variant sickle cell syndromes are discussed separately. (See "Overview of the clinical manifestations of sickle cell disease" and "Diagnosis of sickle cell disorders" and "Overview of the management and prognosis of sickle cell disease" and "Variant sickle cell syndromes".)
INCIDENCE AND SIGNIFICANCE
The gene for sickle cell anemia is widespread throughout the world, being present in Africa, Mediterranean countries (especially Greece), the Middle East, and parts of India.
The prevalence of sickle cell trait is approximately 8 to 10 percent in African Americans [1,2] and as high as 25 to 30 percent in certain areas of western Africa . The Hispanic population is also at risk for sickle cell disease. At least 1 in 180 Hispanic births have sickle cell trait.
There are approximately 2.5 million people in the United States and 300 million in the world who have sickle cell trait (ie, who are heterozygous for the sickle cell gene). The presence of sickle cell trait appears to be protective against severe falciparum malaria, explaining the persistence of this gene in the world population . (See "Protection against malaria in the hemoglobinopathies", section on 'Falciparum malaria and hemoglobin S' and "Protection against malaria in the hemoglobinopathies", section on 'Sickle cell trait'.)