Are There Risks Of Receiving The Radioactive Iodine Uptake Test?

I frequently get asked whether receiving the radioactive iodine uptake test is necessary for people with hyperthyroidism.  For those who are unfamiliar with this test, it is commonly recommended by endocrinologists to help determine whether someone has Graves’ Disease, and can also detect hot or cold nodules, which in turn can suggest whether the nodules are benign or malignant.  To no surprise this test isn’t appropriate for someone who is pregnant or breastfeeding, due to the radiation involved.

With this test, the person is told to swallow a small dosage of radioactive iodine, which is absorbed by the thyroid gland.  The thyroid gland is evaluated six hours later, and then again 24 hours later.  If the uptake is low, then this usually means the person has thyroiditis (inflammation of the thyroid gland), while if the uptake is high and is spread evenly then this suggests the person has Graves’ Disease.  If the uptake is spread unevenly then this usually suggests a multinodular goiter, regardless of whether the uptake is low or high.

Are There Risks When Receiving This Test?

Any test that involves radiation comes with some risk.  It uses a much smaller dosage than radioactive iodine treatment, and so this test is not going to obliterate your thyroid gland.  But this doesn’t mean it’s completely harmless, as if this was the case they would have no problem administering this test to pregnant and lactating women.  So while some people might benefit from receiving this test, I would still be cautious about any test that involves radiation, even if the dosage is small.

The RAI Uptake Test Does Not Confirm The Presence Of Graves’ Disease

Notice that above I wrote that if the uptake is high and spread evenly that this “suggests” the person has Graves’ Disease.  However, the only surefire method of confirming whether someone has Graves’ Disease is by having positive TSH receptor antibodies.  So if someone has positive TSI antibodies, then this 100% confirms that the person has Graves’ Disease.  And if this is the case, then in my opinion the person probably doesn’t need to obtain the radioactive iodine uptake test.

However, while positive TSI antibodies will confirm the presence of Graves’ Disease, these antibodies can fluctuate.  As a result, someone can actually have negative TSH receptor antibodies and still have Graves’ Disease.  If this is the case, then perhaps one can justify getting the radioactive iodine uptake test.  The problem is that if someone has negative TSI antibodies but a high and evenly spread RAI uptake test, this still doesn’t confirm the presence of Graves’ Disease.  So if someone with hyperthyroidism obtains the test for TSI antibodies and it comes out negative, I would recommend waiting one or two months and to get this retested.

But shouldn’t one obtain the radioactive iodine uptake test to determine if they have thyroid nodules?  While this test will confirm the presence of thyroid nodules, so will an ultrasound.  And while there is some controversy over ultrasonic waves and whether exposure to them can affect someone’s health, radiation is known to cause damage to cells, and so I would do everything to avoid it.  And even if the radioactive iodine uptake test reveals the presence of one or more thyroid nodules, a fine needle aspiration will still be necessary to determine whether the nodules are benign or malignant.

Question Your Endocrinologist Before Receiving This Test

Some of my patients have told me that their endocrinologist would not do anything else with them until they received the radioactive iodine uptake test.  In other words, if the patient had positive thyroid blood tests (high Free T3 and Free T4 and low TSH) and wanted to take antithyroid medication to manage the symptoms, some medical doctors have refused to write the patient a prescription until they agreed to receive the RAI uptake test.

I realize this can be a tough situation, but whenever any endocrinologist recommends this test to you, I would ask them the following question: “How will the results of this test affect my treatment recommendations?”.  In most cases they won’t have a good answer.  This is especially true if someone has a positive TSI test.  But even if the test comes out negative, if the thyroid blood tests are positive then typically the treatment options will be antithyroid medication for 18 to 24 months, or radioactive iodine treatment, regardless of whether someone has a low or high uptake test.

Now in some cases the endocrinologist might take a more conservative approach if someone has negative TSI antibodies and a low uptake test.  If this is the case then you might feel like it’s worth getting the test.  In other words, if someone has negative TSI antibodies and the endocrinologist tells you he would recommend antithyroid medication if the RAI uptake test was low, but radioactive iodine treatment if the uptake test was high, then perhaps this would be a good reason to obtain this test.  I of course think that in either situation antithyroid medication should be tried first before radioactive iodine treatment, but that’s just my biased opinion.  Of course another option is to seek the opinion of a different endocrinologist, as some endocrinologists are more aggressive than others.

So hopefully you have a better understanding of the radioactive iodine uptake test, and realize that not everyone with hyperthyroidism needs to obtain this test.  While this test can provide some useful information, one always needs to look at the risks vs. the benefits, and in most cases it is not worth the risk of being exposed to the radioactive iodine, even though it’s a small dosage.  On the other hand, if your endocrinologist can give a good reason why the test is necessary in your situation, then you might decide it’s best to receive it.  So my goal isn’t to try talking you out of obtaining this test, but is just to give you the information you need to make an informed decision on your own.