The thyroid in ulcreative colitis and Crohn's disease. III. The daily fractional turnover of thyroxine.

The daily fractional turnover of thyroxine (T4) labelled with 131 I has been determined in 11 patients with ulcerative colitis (uC) of Crohn's disease and 8 controls. The daily fractional turnover of 131I-T4 was significantly increased in the patient group. The daily total disposal of T4 iodine was not significantly different although it was excessive in 3 of the 11 patients. The amount of T4 in plasma did not differ significantly between the patients and the controls. It is concluded that the T4 metabolism is disturbed in UC and Crohn's disease and that excessive losses of T4 iodine can be a cause of iodine depletion in some patients with longstanding and severe disease.