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Thyroid Level

Posts: 59
Joined: Aug 2009

Would someone please explain exactly what the thyroid numbers represent? For example, T4 T3 etc etc. Shame on me. I am a thyroid cancer survivor, but do not understand my levels. My doctor has become a bit aloof so I thought I ask here. Thank you.

alapah's picture
Posts: 287
Joined: Oct 2009

probably better than I could explain it, though it likely doesn't answer all of your questions - http://www.thyca.org/labtests.htm

Baldy's picture
Posts: 244
Joined: Mar 2011

Hi Emma,

Better than I can explain it, here's the wiki definition of what the thyroid is and does.

"The thyroid gland controls how quickly the body uses energy, makes proteins, and controls how sensitive the body should be to other hormones. It participates in these processes by producing thyroid hormones, the principal ones being triiodothyronine (T3) and thyroxine (T4). These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. T3 and T4 are synthesized from both iodine and tyrosine. The thyroid also produces calcitonin, which plays a role in calcium homeostasis.

Hormonal output from the thyroid is regulated by thyroid-stimulating hormone (TSH) produced by the anterior pituitary, which itself is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus." http://en.wikipedia.org/wiki/Thyroid

Here's the wiki def for T3.

"Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate." http://en.wikipedia.org/wiki/Triiodothyronine

And here's the wiki def for T4.

"T4 is involved in controlling the rate of metabolic processes in the body and influencing physical development. Administration of thyroxine has been shown to significantly increase the concentration of nerve growth factor in the brains of adult mice.

Thyroxine is a prohormone and a reservoir for the active thyroid hormone triiodothyronine (T3), which is about four times more potent. T4 is converted in the tissues by deiodinases, including thyroid hormone iodine peroxidase (TPO), to T3." http://en.wikipedia.org/wiki/Thyroxine

According to some lab results I had done recently, the normal ranges are ...

TSH 0.4 to 4.5 uiU/ml
Thyroglobulin 2.0 to 35.0 ng/mL
Thyroglobulin AB less than 20 IU/mL [AB=Antibodies]
T4, Free, Non-Dialysis 0.8 to 1.8 ng/dL

This is not all that you can be tested for and I think different labs will go by slightly different levels {at least they have for me.} There is also more than one way to test some of these levels, but I think they use different units.

I also wonder if there is such a thing as a 'normal' range. Judging from some of the accounts of the people using this web site, it's possible to have a lot of side effects and yet still test normal. Maybe it would be best to say, "Normal for the majority of people."

Hope this helps,

Posts: 59
Joined: Aug 2009

Thank you so much for taking the time to answer my question. I do understand it better now.

Posts: 5
Joined: May 2011

Hi Emma,

Everything that Alan said plus:

The levels that your Dr's want you to have may be different depending on your situation. If you still have some thyroid function you want your levels to be within the normal ranges. But if your cancer was agressive and they removed the whole thyroid and want to prevent it from coming back (which is my case) they usually want your TSH to be 0 and your T4 to be either in the high range of normal or above normal. The reason being TSH signals the body to produce T4 and T3 which would stimulate the production of more thyroid cells. If they are in fear of the cancer returning, having your T4 levels high would supress the production of TSH in the pituitary gland. In my case, if my T4 is high but my TSH is above 0, the cancer is returning and is agressive because the I have working throid cells in spite of the high T4 and I would need another round of RAI and maybe even direct radiation.

My doctor doesn't really look at my T3 level that much (although it is on my lab sheet for my next visit).

I guess the most important thing about the difference between T3 and T4 is is that T3 is what your tissues actually use for metabolism. T4 has to be converted to T3 by a enzyme in the liver. The throid gland directly produces 20% of the body's T3 and the other 80% in converted.

I just read an article that said a combnation of T3 and T4 is the best therapy. It's been two years for me trying to get my levels right. My T4 is where it needs to be but I still feel like crap. I do know that when on cytomel, which is T3, before and after RAI I feel awesome. The article reccomended 5-12.5 mg of cytomel twice a day in addition to T4 (synthroid/levothyroine) if the T4 levels are where they need to be and the patients either has a low T3 level or a normal T3 level but is still having hypo symptoms.

I hope this helps.


Posts: 59
Joined: Aug 2009

Thank you Ashley for answering my question. My situation is exactly like yours. I am on Synthroid and Cytomel now, but I am exhausted. I think I will ask the dr. to up the Cytomel, since I am only taking 5MCG twice a day, maybe it should be a bit higher. Thanks for the insight.

Posts: 507
Joined: Apr 2010

Myself I am about 300 lbs (i go up and down about 10 lbs)

I am on 200 mgs/day Synthroid and 25 mgs/day of cytomel (12.5 2x/day)

I am glad to hear I am not the only one on a synthroid cytomel combination (I think it works much better than just synthroid)


Posts: 55
Joined: Nov 2009


Thank you for the information. I am almost two years out of a Hurthle Cell Carcinoma stage 3 diagnosis. Though my scans are clear, my stimulated thyroglobulin is in a danger zone according to my dr. I have all hypo symptoms though my TSH is .012. My dr. is not willing to increase my Synthroid due to the low TSH, so this might be my answer if he is willing! Thank you so much for sharing.


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