Sickle cell tests are used to detect, diagnose, and confirm sickle cell anemia (also called sickle cell disease). Sickle cell anemia is an inherited disorder that leads to the production of an abnormal hemoglobin variant, hemoglobin S (HbS or HgbS). In the red blood cell (RBC), this variant can form polymers, changing the shape of the RBC from a round disc to a characteristic crescent (sickle) shape. This altered shape limits the RBC’s ability to flow smoothly throughout the body, limits the hemoglobin’s ability to transport oxygen, and decreases the RBCs lifespan from 120 days to about 10-20 days. The affected person can become anemic because the body cannot produce RBCs as fast as they are destroyed; the person can suffer painful episodes and a variety of complications when sickled cells become lodged in, and obstruct, small blood vessels.

Hemoglobin S production arises from an altered (mutated) “S” gene. A person with one altered S gene will have sickle cell trait. The person does not generally have any symptoms or health problems but can pass the gene on to his children. When a person has two copies of the S gene (homozygous SS), he has sickle cell anemia. Someone who has one S gene and one of a variety of other hemoglobin variants is said to be doubly heterozygous. This person can also experience symptoms and complications from sickled cells.