Sickle cell tests are used to identify the presence of hemoglobin S, to evaluate the status and number of a person's red blood cells (RBCs) as well as hemoglobin level, and/or to determine whether a person has one or more altered hemoglobin gene copies.ickle cell tests are used to identify the presence of hemoglobin S, to evaluate the status and number of a person's red blood cells (RBCs) as well as hemoglobin level, and/or to determine whether a person has one or more altered hemoglobin gene copies.