Answer to Question #10524 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — Diagnostic Nuclear Medicine

The following question was answered by an expert in the appropriate field:

Q
My thyroid stimulating hormone (TSH) levels indicate that I might have an underactive thyroid. My doctor told me to have a diagnostic test with a radionuclide.
If I'm trying to conceive, how long do I need to wait after a diagnostic dosage of radionuclide?

My family practice doctor wasn't able to answer my question about the effect of radionuclides on a planned pregnancy, and I can't find the answer on the Internet. Of course, I know it's not allowed during pregnancy, but how long of a time is safe after the examination?
A
What to do about an elevated TSH? The next step would probably be to get a thyroid function panel, which is a blood test. If your thyroid hormone levels are low, which is suggested by an elevated TSH, then the thing to do is give you thyroid pills to get you to a normal hormone level. Many people become hypothyroid from autoimmune thyroid disease (Hashimoto's thyroiditis). There's nothing you can do about it and it's not a serious problem because you can take thyroid hormone pills to correct it. If you are on thyroid hormone pills and get pregnant, it is common that in the second or third trimester you may need a little more. After the baby is born, you drop back to your previous nonpregnant dose.

It isn't necessary to get a thyroid scan with a radionuclide because you have an elevated TSH, but even if you do get one, the radiation dose is so low that you don't have to worry about it. Almost all diagnostic nuclear medicine tests are commonly performed during pregnancy, with the exception of those using iodine-131, which is avoidable.

I don't know what your medical plan provides for, but you should probably be seeing an endocrinologist, or at least an internist, for your thyroid problem.

Carol S. Marcus, PhD, MD
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