Auto regulatory capacity of the thyroid gland after numerous iodinated contrast media investigations.

Excess of iodine may interfere with thyroid function. It is unclear to what extent the thyroid function is disturbed by repeated infusion of iodide contrast agent (IC) used during X-ray examinations. Thyroid function tests free T4 (FT4), free FT3 (FT3), thyroid-stimulating hormone (TSH), TSH receptor antibodies (TRAb) and thyroid peroxidase antibodies (TPO-Ab) were measured in a group of Norwegian patients with an assumed normal iodine balance before, 1 and 6 weeks after IC infusion. Forty patients (19 females and 21 men) referred for routine CT were included. Thirty two out of 40 patients had previously undertaken IC investigations. The mean TSH concentration was 2.1 mIU/l ± 1.7 at the baseline, increased to 2.9 ± 2.5 after 1 week (p < .001), and reverted to nearly initial values 1.4 ± 0.8 after 6 weeks. Initially the mean FT4 was 14.1 pmol/l ± 1.9 FT4, reduced to 13.3 pmol/l ± 2.5 (p = .009) after 1 week, and returned to 14.0 pmol/l ± 2.5 after 6 weeks, comparable to the initial values (p > .05). FT3 levels did not change during the period. There was no relationship between FT4, or TSH and age, gender, cancer/not cancer, number or frequency of earlier IC investigations. In conclusion, IC induces changes in thyroid function tests, however, they return to normal levels after 6 weeks. Our results suggest adequate auto regulatory capacity of the thyroid gland even in those with repeated contrast investigations (up to 40). Routine testing of thyroid function should therefore not be undertaken in this patient group.