The FDA issued a safety announcement on Nov. 17 warning that, in rare cases, infants have been reported to have underactive thyroid after using contrast media containing iodine for x-rays and other imaging procedures.

Between 1969 and early 2012, there were 10 cases of underactive thyroid in infants younger than four months who received iodinated contrast media (ICM), according to the FDA’s adverse event reporting system database. There was also one case of underactive thyroid in an adult.

The FDA approved changes to the labels of all ICM products, although the agency said it does not recommend changing prescribing, administration or monitoring practices.

The FDA plans on investigating the issue further and has required manufacturers of ICM products to conduct studies to investigate the potential safety problems.

Of the 10 infants who had underactive thyroid, six were born full-term with cardiac abnormalities and four were born prematurely. The average time to hypothyroidism diagnosis was 15 days.

Seven of the infants had hypothyroidism after intravenous ICM administration, while hypothyroidism occurred once via rectal ICM administration, once via rectal and intravascular administration and once through the breast milk of a mother receiving intravenous ICM. In four cases, infants also took a topical iodine product.

Eight of the 10 infants had clinical improvement, and there were no outcomes reported in the other two cases. In addition, four infants received treatment for hypothyroidism: one had treatment for six months, one had treatment for 10 months, one had treatment for an unspecified amount of time and one died from other causes while being treated for hypothyroidism.

The FDA also cited a report in 2014 that found three infants with congenital heart disease developed hypothyroidism after exposure to ICM and iodine in surgical dressings.