Researchers found that people who were administered a common iodide contrast agent during medical scans are more likely to develop thyroid disease than a control group.
Iodinated contrast media is commonly administered to millions of patients each year undergoing CT scans, cardiac catheterizations and other angiograms to allow doctors to see blood vessels and tissues.
For this study, the researchers from the Harvard Medical School and Brigham and Women’s Hospital followed nearly 2,000 people without a history of thyroid dysfunction over a 20-year period. During that time, 178 patients developed hyperthyroidism and 213 patients experienced a low functioning thyroid (hypothyroidism).
Those who developed hyperthyroidism were two and a half times as likely to have been injected with an iodide contrast agent. The likelihood of exposure was three times as great for those with hypothyroidism.
Despite common knowledge that high levels of iodide can disrupt thyroid function, the researchers were surprised by the strong association between iodinated contrast media and thyroid disease. They are particularly concerned about the results because iodinated contrast media is so widely used.
The study authors point out that these findings do not suggest that people should not have tests that use iodide agents as there are some situations where they are medically necessary. Rather, they say these findings give doctors and patients a better understanding of the risks involved so they can better weigh the risks vs. benefits of these tests.
When the situation is not life threatening or the doctor is already 99% sure of their diagnosis, iodide contrast tests may not be advisable. If these tests are medically necessary, doctors may need to monitor a patient’s thyroid function for some time following the procedure.
It’s important to note that the study results do not apply to M.R.I.s which do not use iodinated media or to dyes given orally for GI imaging.
For more on thyroid health, read Nutrition for Thyroid Health: Foods that Help and Harm.
Sources:
Science Daily
New York Times
Archives of Internal Medicine