Which thyroid disorders are associated with the use of iodine-based contrast media? Which patient groups are at the highest risk? What are the contraindications to this test?

In some individuals, the use of iodine-based contrast media can lead to the development of hypo- or hyperthyroidism, as well as a life-threatening thyroid storm. This is associated with the high amount of iodine in the contrast material (significantly higher than the physiological demand), genetic predisposition toward autoimmune thyroid diseases, dietary intake of iodine, or the presence of risk factors, such as certain thyroid diseases.

Nodular goiter in subclinical hyperthyroidism or euthyroidism, as well as latent Graves disease (rare cause) are associated with an increased risk of hyperthyroidism following the use of iodine-based contrast media. Active hyperthyroidism (decreased thyroid-stimulating hormone [TSH] levels, elevated free thyroxine [FT] 4 and / or FT3 levels) is a contraindication to the administration of iodine-based contrast material.1,2

The risk of hypothyroidism following the use of iodine-based contrast media is higher in the cases of chronic autoimmune thyroiditis and in the patients with a history of postpartum (lymphocytic) thyroiditis or subacute thyroiditis, amiodarone-induced type 2 hyperthyroidism, and treatment with interferon-α. The risk is also increased in the patients who underwent partial thyroidectomy. However, neither hypothyroidism nor its management or an increased risk of its development are contraindications to a contrast-enhanced imaging test.

Thyroid disorders induced by the use of iodine-based contrast media occur in about 1% to 15% of the patients who underwent an imaging test with the use of such media. Elderly individuals, patients with increased cardiovascular risk, as well as those with renal failure are also at a higher risk of developing a thyroid disease following the administration of iodine-based contrast material.

Assessment of the TSH concentration before a contrast-enhanced imaging test is particularly indicated in those patients. If the TSH levels are within the normal range, the patients should be monitored for symptoms suggestive of thyroid dysfunction.

Of note, most of the thyroid disorders that develop following the use of iodine-based contrast media are mild and transient, and life-threatening complications (thyroid storm) occur rarely.

Do patients with hypothyroidism need to be specifically prepared for a contrast-enhanced computed tomography examination, and do they require monitoring afterwards?

Imaging tests involving the administration of iodine-based contrast media can be performed in patients with both subclinical (elevated TSH levels, normal FT4 levels) and overt hypothyroidism (elevated TSH levels, decreased FT4 levels).

However, if hypothyroidism has been diagnosed recently, causative diagnostics should be extended (if this is not possible, the patient should be referred to an endocrinologist), with initiation of the treatment, and monitoring of the TSH level (in the patients with primary hypothyroidism; in the case of secondary hypothyroidism, FT4 level monitoring is also required) every 4 to 6 weeks. In the patients with an established diagnosis of hypothyroidism, and treated with levothyroxine, only routine follow-up is required.1,2