Diagnosis of hyperthyroidism when serum-thyroxine alone is raised.

31 patients admitted to hospital with different non-thyroidal intercurrent diseases were found to have raised total serum-thyroxine (T4) and free T4 together with normal serum-triiodothyronine (T3) concentrations. At admission none was clinically hyperthyroid. Patients were assigned to 3 groups according to clinical course and the laboratory findings. In the first group (14 patients) classic hyperthyroidism developed after recovery from the intercurrent disease. 11 out of these 14 patients had recently received iodine-containing preparations. In a second group (11 patients) the initially raised serum-T4 rapidly returned to normal with recovery from the non-thyroidal disease. In a third group (6 patients) serum-T4 concentrations remained raised well after recovery from intercurrent disease. In this group, there were 2 cases of transient iodine-induced (Jod-Basedow) hyperthyroidism in which raised serum-T4 returned spontaneously to normal after several months as iodine was eliminated. These results indicate that increase in serum-T4 with normal serum-T3 in patients with intercurrent systemic disease is not always the result of hyperthyroidism and in many cases probably reflects changes in peripheral metabolism of T4. It is suggested that careful clinical follow-up is needed in patients with raised serum-T4 and normal serum-T3 for the early detection and treatment of classic hyperthyroidism.