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Iodine for Scans Triggers Hyperthyroidism

Have you ever had a CT scan or an X-ray with contrast? You may have received iodine for scans. It's cheap and effective but it can trigger hyperthyroidism.

Americans undergo an enormous number of scans each year. Experts estimate that over 80 million CT scans are performed annually. That doesn’t include other scans such as coronary angiography, arthrography or myelography. Physicians often order contrast media to be injected during the X-ray exposure to enhance the clarity of the images and help with the diagnosis. There is, however, a downside to using contrast containing iodine for scans. A big dose of iodine can trigger HYPERthyroidism or HYPOthyroidism. In other words, contrast material used in CT scans and X-ray images can knock your thyroid out of whack. Moreover, kidneys may also suffer as a result of such iodine exposure. Is there a way to protect the kidneys?

Could a Simple Supplement Shield the Kidneys?

Q. Would you please write about using N-acetylcysteine to protect the kidneys from contrast dye damage during CT scans? Doctors seem to order iodine for scans more and more. To me it seems like NAC would be a simple thing to take to prevent kidney damage. No one seems to be talking about it, so I wonder if I am way off base.

A. Iodine-containing contrast medium (ICCM) is used to make scans more effective. Radiologists inject ICCM during coronary angiography to visualize artery pathology. They may also use it during scans of joints, the spine or digestive tract.

While ICCM can make scans clearer, some people react badly to it. They may suffer allergic reactions, problems with the thyroid gland or kidney injury.

You are correct that NAC (N-acetylcysteine) has been shown to help protect the kidneys from damage caused by iodine dye (International Urology and Nephrology, Jan. 3, 2023). This dietary supplement is available over the counter and is also used to counteract acetaminophen overdose.

Hyperthyroidism After Iodine:

Q. I injured my shoulder and two months later I had an arthrogram with iodine dye. Now I have heart palpitations, anxiety, dizziness and adrenaline rushes from hyperthyroidism.

I have seen an endocrinologist for the hyperthyroidism. She said I’ll need to wait six months after the arthrogram to be tested for excess thyroid. If my blood test doesn’t normalize, I may need to take methimazole. This drug can have serious side effects. Am I right that the iodine dye is probably to blame for my hyperthyroidism?

A. Diagnostic imaging such as CT scans or arthrography with iodine contrast media can trigger hyperthyroidism (Journal of Clinical Endocrinology and Metabolism, Feb. 2015).  Many health professionals are unaware of this complication. If they have heard of it at all, the assumption has been that it is extremely rare.

An Unappreciated Risk of Iodine for Scans:

When iodine is injected during a scan or during angiography the material is referred to as iodinated contrast media (ICM). To give you some idea of the dose involved we need to consider the recommended daily intake of iodine. It is 150 micrograms. That’s not much. It’s less than 1/5 of a milligram.

Now consider the dose of a typical ICM injection during a CT scan. Some experts estimate that it ranges from “2,500 to 5,000 micrograms of bioavailable free iodine and 15 to 37 grams of total iodine” (Journal of Clinical Endocrinology and Metabolism, Feb. 2015).

Another group of researchers described the ICM dose this way (Archives of Internal Medicine, Jan. 23, 2012).

“A typical dose of ICM contains approximately 13,500 micrograms of free iodide and 15 to 60 grams of bound iodine that may be liberated as free iodide in the body. This represents an acute idodide load of 90 to several hundred thousand times the recommended daily intake of 150 micrograms. Sudden exposure to high iodide loads, given in other contexts, can disrupt thyroid hormone regulations, resulting in hypothyroidism (Wolff-Chaikoff effect) or hyperthyroidism (Jod-Basedow).”

Symptoms of Hyperthyroidism:

Imagine drinking 5 cups of coffee all at once. Your metabolism would rev up. Some people describe hyperthyroidism as something akin to having their internal motor going way too fast.

  • Weight loss even after eating normally
  • Rapid pulse, sometimes exceeding 100 bpm without exercising; heart palpitations
  • Frequent bowel movements
  • Hand tremor
  • Feelings of being wired or overly caffeinated
  • Alterations in energy from fatigue to exhaustion
  • Hives or itching
  • Changes in vision, bulging eyes
  • Anxiety; difficulty sleeping
  • Cognitive impairment; confusion, scrambled brain effect

The Diagnostic Dilemma:

When physicians determine that people need CTs with contrast, that usually means iodine will be injected. It is relatively inexpensive and quite effective.

If a patient starts losing weight, feeling jittery or going to the bathroom four or five times a day, it may be linked to the iodine used in the scan or the coronary angiography. And if a person starts suffering symptoms of hypothyroidism several weeks after a scan, that too may be connected to the diagnostic procedure.

However, very few people who undergo a scan will be tested for hyper or hypothyroidism over the next few months. It takes a pretty good medical sleuth to figure this out. The effects of the excess iodine can last for several months or even a year or two. Some people may never return to normal thyroid function without medical treatment.

What to Do for Hyperthyroidism?

Your endocrinologist will need to track your thyroid function very carefully. She may need to prescribe a beta blocker to control your heart palpitations and adrenaline rushes until the iodine effect begins to wear off. You may also need to take an anti-thyroid medication such as methimazole if your thyroid gland does not calm down on its own. A low dose might not be as scary as it seems if you are monitored carefully.

Methimazole Side Effects:

  • Skin rash and/or itching
  • Digestive distress (nausea, indigestion, vomiting, changes in taste)
  • Joint pain, arthritis, muscle pain
  • Headache
  • Hair loss
  • Drowsiness, dizziness
  • Blood disorders, liver toxicity, kidney damage

The People’s Pharmacy Perspective:

Physicians who order iodine for scans need to be vigilant. Older people are especially vulnerable to hyper and hypothyroidism after such iodine exposure. Younger patients are not immune to this reaction, either.

If you need a scan with contrast, ask about taking NAC for kidney protection. Afterwards, be on the look-out for signs of thyroid dysfunction. If symptoms occur, it is imperative that thyroid tests be performed promptly and appropriate treatment initiated until the thyroid gland recovers from the excess exposure to iodine.

Have you experienced symptoms after a scan with contrast? Please share your story in the comment section below.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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  • Cepaityte D et al, "N-Acetylcysteine: more than preventing contrast-induced nephropathy in uremic patients—focus on the antioxidant and anti-inflammatory properties." International Urology and Nephrology, Jan. 3, 2023. doi: 10.1007/s11255-022-03455-3
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