According to the Mayo Clinic, an ANA titer, or test, determines if there are antinuclear antibodies in a person's blood. If these antibodies are present, then the ANA titer comes back positive. A positive ANA test is indicative of an autoimmune disorder.
In the majority of cases, a positive ANA test indicates that autoantibodies are being produced in the patient's blood. In some cases these autoantibodies attack the patient's own cells and cause an autoimmune disorder to begin. However, the Mayo Clinic also states that some people do have positive ANA tests without having an autoimmune disease. The test is ordered when a doctor suspects an autoimmune disorder.