Hemoglobin S, HbS is seen when the sickle cell anemia trait is present. It is a mutation of the beta globin gene. Beta globin combines with alpha globin to form hemoglobin. Hemoglobin C, HbC is also a mutation of the beta globin gene. A carrier of both will have the condition of one with sickle cells trait, but possibly also a mild anemia caused by the HbC. Some people with sickle trait can have symptoms and even a sickle crisis under certain conditions, such as high altitude, high temperatures and intensive exercise. Some never have any issues.
When a family member carries any mutation of the alpha or beta globin genes, all family members should be tested, especially anyone who may have children in the future. One sickle gene is usually not a major problem, but when two people with the trait have a child, there is a 25% chance that the child will carry two sickle genes and have the major form of the disease. This fact makes it necessary to be tested and for partners to be tested, if one does prove to be a carrier.