Thyroid under contrast: Unveiling the effect of radiographic iodinated contrast media on thyroid function tests

BACKGROUND Iodinated contrast media (ICM) used in radiographic imaging can alter thyroid hormone levels due to their high iodine content, potentially impacting thyroid function, especially in susceptible individuals. This study aimed to evaluate the effects of ICM on thyroid function tests including T3, T4, and TSH. METHODOLOGY A total of 422 consecutive patients undergoing contrast-enhanced computed tomography and interventional radiological procedures with iodinated contrast were included in this prospective observational study in our hospital from 2022 to 2025. Baseline thyroid function tests were obtained prior to contrast administration, and follow-up tests performed 3–4 weeks post-exposure. Data was analyzed using paired t-tests and Wilcoxon signed-rank tests. RESULTS Post-contrast administration, there was statistically significant increase in T3 (mean pre: 1.37 ± 0.34 to post: 1.53 ± 0.38, p < 0.001) and T4 levels (mean pre: 8.27 ± 2.01 to post: 9.66 ± 2.63, p < 0.001), with a slight but significant decrease in TSH (mean pre: 3.42 ± 1.37 to post: 3.24 ± 1.66, p = 0.001). Changes were more pronounced in patients with pre-existing hyperthyroidism and hypothyroidism. CONCLUSION Iodinated contrast media exert measurable effects on the hypothalamic–pituitary–thyroid axis, with disproportionately greater impact in individuals with pre-existing thyroid disorders. Exposure to ICM is associated with transient elevations in circulating T3 and T4 alongside suppression of TSH. While euthyroid individuals generally experience mild, self-limited effect, this may be clinically relevant in susceptible populations. These findings support systematic risk stratification and interval biochemical monitoring for those undergoing contrast imaging, with heightened vigilance in those with underlying thyroid disease.