Alterations in thyroxine metabolism in Crohn's disease.

To evaluate the possible alterations in thyroxine metabolism in patients with Crohn's disease (C.D.), the serum concentrations of thyroxine (T4), triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), and thyroxine binding globulin (TBG) were determined in 23 patients with C.D. and in 25 healthy controls. While concentrations of T4 and rT3 in patients with C.D. were similar to those seen in healthy controls, serum T3 was lower in patients with C.D. (0.93 +/- 0.4 ng/ml) than in controls (1.20 +/- 0.3 ng/ml, p less than 0.005). TBG concentrations were elevated in two patients with C.D., and below normal in two others. However, the group mean of TBG concentrations in patients with C.D. (23.7 +/- 6.9 micrograms/ml) was similar to that of healthy controls (21.9 +/- 3.6 micrograms/ml, p greater than 0.05). Changes in peripheral deiodination of thyroxine, enhanced in some cases by treatment with glucocorticoids and/or increased turnover of T3 may be the cause of the decreased concentration of T3 in some patients with Crohn's disease.