Do Iodine-Containing Contrast Media Induce Clinically Relevant Changes in Thyroid Function Parameters of Euthyroid Patients Within the First Week?

Little is known about the reaction of normal thyroid glands to the iodine load given by x-ray dyes. We have therefore investigated the short-term effects of high doses of iodine on thyroid parameters in euthyroid patients. We measured free triiodothyronine (FT₃), free thyroxine (FT₄), and thyrotropin (TSH) serum concentrations before and daily for 1 week after parenteral application of x-ray dyes (coronary angiography: n = 16; computed tomography [CT] of either thorax or abdomen: n = 6; iodine dose range from 300–1221 mg of iodine per kilogram). Inclusion criteria were as follows: normal FT₄, normal TSH, negative thyroid antibodies, urinary iodine excretion below 30 μg/dL, no palpable goiter and no euthyroid sick syndrome. All but one patient reacted with a TSH increase. Mean TSH values increased significantly 3–5 days after the iodine load within the normal range. Four patients (18%) had a TSH increase above normal, the maximal observed value being 6.4 μU/mL. Basal TSH values of these four patients were above 2 μU/mL. The day peak TSH concentrations were reached varied from day 1 to day 7, the majority (32%) having the peak on day 3. Peak TSH was significantly correlated with basal TSH values (r = 0.794, p < 0.0001). FT₄ and FT₃ remained unchanged and there was no significant correlation between the dose of iodine and the TSH reaction. In conclusion, iodine-containing contrast media can induce transiently subclinical hypothyroidism even in euthyroid patients. The TSH reaction seems to depend on the preexisting state of thyroid function.