Thyroid UK
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How "bad" do my levels need to get to do the Radioactive Iodine Therapy. And is it T3, T4 and TSH or which levels are they watching?

I'm 2 wks post TT with Stage 3 Papillary cancer. They told me we had to wait for my levels to get "bad" to do the Radioactive Iodine Therapy. I just had labs done. My TSH is 24.42 mcIU/mL (ref range 0.3 - 5.0), T4 is 3.54 mcg/dL (4.50 - 11.70), T3 Total is 0.7 ng/mL (0.8 - 2.0). They won't start replacement therapy until the RAIT is completed so just wondering what numbers we are watching and if there is a typical range when they are "bad" enough that the cancer will ready to absorb the radioactive iodine?

9 Replies


It is the TSH they are watching. I had a TT in March for papillary Cancer, was then put immediately onto liothyronine (T3) for 6 weeks and then stopped it for 10 days to cause my TSH to to rise. I then had my RAI on last Wednesday. As part of the process you have to follow a low iodine diet for a minimum of 2 weeks to deplete any stores within the body. It is this lack of iodine in the body and the raised TSH which helps ensure that any remaining thyroid cells will take up the radioactive iodine and be destroyed. If you are in the Uk there are guidelines that should be followed.

There was a multi centre random controlled trial run in early 2000's which now results in a lower treatment dose of radiation than before depending on the size of the tumour and degree of any spread. (Sorry can't find the link at present, but it was coordinated from Newcastle)

I wish you well on the road to recovery. Be kind to yourself you will still be feeling the effects of the surgery. Best wishes.

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Yes as stated its that high TSH they're wanting, along with a body starved of iodine.

My my went through this and I can say it was hell watching her suffer each day without her T4. Hang in there, try to get family/friends to help support you, do some nice things for yourself. The more you can adhere to no T4 and the low iodine diet, the better the chances that the RAI treatment has success.

The RAI treatment itself & aftermath wasn't too bad. Mostly boring whilst she was meant to be isolated, as she's a social butterfly normally.

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Your TSH needs to be over 30. My RAI was 2.5 months after TT but I was on T3 meds which were stopped 2 weeks prior to RAI, so hopefully you won't have much longer to wait.


Thanks Clutter. I appreciate the information. I have been trying to find out what the target number was and I have had a number of issues already which made my doctor think my body may have responded quicker to the removal of my thyroid than the "normal" 4+ weeks that he said it would take. I hadn't even started the Low Iodine Diet yet so I'm starting it immediately to improve my chances of success. Thanks!



You might find this link useful

I hope everything goes well.


Hi, cjrsquared and CatSlave, and thanks for your informative and supportive responses.

I'm not in the UK, cjrsquared, but I do greatly appreciate the link to the Guidelines. I've read through some of it just now and it looks to be very informative and answered my question to give me a reference point. As knowledge is power and I believe we have to empower ourselves as we are our own best advocate so this Guide will be very helpful. Doesn't matter what land our feet walk each day, our bodies all work the same way and long ago I learned doctors are human and can make mistakes or be wrong so I need to research the information available so that I can ask and question the doctor's advice intelligently if it doesn't sound right.

As an example, my doctor doesn't think I need to go on the low iodine diet and everyone I've spoken with or read has talked about the importance of starving the cancer for the iodine and how the LID helps do this. I want to give my body the very best chance of ablating the cancer cells especially since they have already metastasized and are in my lymph nodes so... research time and time to start questioning more of what he says.

Thank you both again and I wish you and yours Good Health!


dear NatureArtistCLD, you don't do the low iodine diet if not plan for a RAI treatment within two or tree weeks. and you should know that in a lot of countries they don't do RAI for thyroid cancer anymore, I was offer not to have it here in the UK, but chose to have it.


Thank you for the info, hay06. I have a lot of scar tissue in my neck as a result of a previous neck surgery years ago so the surgeon had to leave some large pieces of my thyroid and more of the cancerous lymphs buried in the hardened scar tissue so the only way to get at it is with high dose radiation. Blood work showed I was almost at a TSH of 90 but my TG labs showed definitely large pieces left so we went ahead with the RAI. I'm done with the isolation and have started on levothyroxine now so waiting to see my endocrinologist in another week to discuss post body scan.

He had said that he normally doesn't recommend the RAI except for the unusual circumstances in my case due to the scar tissue. I was happy to find an endocrinologist that specializes in thyroid cancer.


Hi NatureArtist,

Hopefully the RAI uptake will have been good and destroyed any remaining thyroid cells. My follow up whole body scan was 5 months after the original RAI. It meant coming of Levothyroxne 4 weeks prior but Liothyronine (T3) was prescribed for the first 2 weeks. LID and no meds for the two weeks prior to RAI was hard. The dose was 30mCi as opposed to the 100mCi first time and no quarantine although restrictions still apply.


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