The measurement of complement fixation by autoantibodies directed against thyroid membrane antigens.

This paper describes the use of sensitized sheep red blood cells for the detection and titration of complement fixation by autoantibodies directed against human thyroid membranes in the serum of patients with autoimmune thyroid disease. Patients with elevated circulating levels of TPO antibodies and diagnosed as having autoimmune hypothyroidism (including Hashimoto's disease) or autoimmune hyperthyroidism (Graves' disease) were studied. Complement fixation titres were highest in those patients with autoimmune hypothyroidism compared with the autoimmune hyperthyroid group. Serum samples obtained from a group of patients with thyroid neoplasia and from normal healthy volunteers were negative in this test. The TPO antibody activity when "corrected" for its CF potency suggests that the autoantibodies found in autoimmune hypothyroidism are potentially more destructive than those found in the non-destructive autoimmune thyroid diseases.