One of every 600 black people in the United States has sickle cell anemia. In addition, sickle cell–hemoglobin C disease and sickle cell–β-thalassemia, which are other common genotypes of sickle cell disease, together are as common as sickle cell anemia. Sickle hemoglobin (hemoglobin S, α₂ β₂S) accounts for over half the hemoglobin in patients with these disorders. Eight percent of black Americans are heterozygous carriers of the sickle cell trait; about 40 percent of their hemoglobin is hemoglobin S. They do not have anemia and need neither treatment nor occupational restrictions. About 5 percent have hematuria at . . .