Effects of iodine contrast media on thyroid function – a prospective study

Objectives: When exposed to iodine contrast medium (ICM), thyroid dysfunction may develop, due to excess amounts of iodide. The incidence of contrast-induced thyroid dysfunction has been difficult to interpret, because of the observational and retrospective designs of most previous studies. With the Swedish CArdioPulmonary bioImage Study (SCAPIS), where randomly selected individuals aged 50–65 years, underwent contrast-enhanced coronary CT angiography (CCTA), we were able to prospectively assess the incidence, magnitude and clinical impact of contrast-induced thyroid dysfunction. Methods: In 422 individuals, thyroid hormone levels were analysed before and 4–12 weeks after CCTA. Thyroid-related patient-reported outcome questionnaires (ThyPRO) at the time of pre and post-CCTA blood samplings were provided by 368 of those individuals. Thyroid peroxidase antibodies (TPOab) were analysed and an ultrasound of the thyroid gland was performed to detect any thyroid nodules. Results: There was a small statistically significant effect on thyroid hormone levels but no cases of overt hypo- or hyperthyroidism after ICM. Subclinical hypo- or hyperthyroidism or isolated low/high levels of free thyroxine (fT4) developed in 3.5% of the population with normal hormone levels pre-CCTA but without any increased thyroid-related symptoms compared to the remaining cohort. Elevated TPOab and being born outside Sweden were risk factors for developing subclinical hypothyroidism. The presence of thyroid nodules was not associated with ICM-induced thyroid dysfunction. Conclusion: The results of this prospective study support the notion that in iodine-sufficient countries, ICM-associated thyroid dysfunction is rare, usually mild, self-limiting and oligo/asymptomatic in subjects aged 50–65 years.