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123-Iodine sodium for thyroid imaging scan

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  • 123-Iodine sodium for thyroid imaging scan

    How long does my client have to interrupt breastfeeding if she is administered this radioactive substance? The scan is to determine whether she has thyroiditis or Graves disease. The dose is usually 300 microcuries (0.3 millicuries) but they can give 150 microcuries (0.15 millicuries) if necessary...the test will just take longer. She would prefer to use the smaller dose, of course. Medications and Mother's Milk 2014 says that a dose of 0.4 millicuries would require complete cessation of breastfeeding or until counts are baseline. It seems cost-prohibitive to send breastmilk to a nuclear medicine lab if the answer is out there somewhere.
    If the half life is 13.2 hrs, then 5 half lives would be 2.75 days but it seems that the cessation time is dose dependent. The client is having the test done Monday, Aug 3 so I am looking forward to your answer.

  • #2
    Annie:

    While I-123 does have a short 13 hour half life, it decays to a radioisotope with a 4 day half life (I-124). We generally suggest mothers pump and discard their milk following I-123 for about 66 hours, and then return to breastfeeding, as most of the radioisotope is eliminated in the urine. I understand it is difficult to get milk 'counted', thus we pick what we consider a safe waiting period of 66 hours. Other forms of I-123 such as hippurate salts are rapidly cleared by the kidneys and do not attach to the thyroid gland, hence moms can presumably return to breastfeeding earlier...but this is only with a rapidly clearing I-123 hippurate.

    I'd suggest she pump and discard for 66 hours following her procedure with I-123.

    Tom Hale Ph.D.

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    • #3
      Thank you for this information. She will share it with her radiologist. However, I read in LactMed that a woman who is administered less than 0.4miCu does not need to avoid physical contact with her baby so it must be dose dependent. If they use 0.15miCu, wouldn't it clear her body faster than 0.4? Or does the amount of the isotope not matter?
      And how should she dispose of her contaminated milk (or waste products) to protect the environment? I know that some hospitals have separate toilet facilities for clients being treated with radioactive substances but how does that work for those who are at home? Thanks in advance for your thoughts on this.
      Annie Brown, FNP, IBCLC

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      • #4
        Annie:

        Dose does matter, particularly with radioisotopes, as it determines the radioactive exposure to mom and infant. If she is only receiving 0.15 miCu, then the risk is reduced but not completely. But I suggest that a breastfeeding interruption and limited close contact of 2-3 days is important. We don't have a lot of good data concerning radioisotope exposure in infants. I've read all this literature, and its obscure and conflicting. My suggestion is to avoid ALL unnecessary exposure if possible. Have the mom save up milk beforehand. Have her buy some donor milk. Have her use formula, but don't have her expose her infant to radiation if there is any way out of it. Avoiding exposure is a small price to pay to avoid ALL risk of thyroid cancer in her infant.

        If it were my baby, I'd avoid extensive close contact and using my own milk for 3 days.

        As for destruction of the milk. She could freeze it in her freezer for a week and then use it, or dispose down the toilet. It will be totally decayed in a week or so.

        Tom Hale Ph.D.

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