Very Low TSH

[bated]

I have been successfully treated for hypothyroidism for several years.  My TSH, Free T4 and Free T3 are tested every three months.  Everything has come back in the normal range until my last tests on 4/22.  My TSH is very low, however the T4 is at the very bottom of the reference range and the T3 is right in the middle of the reference range.

In January it was discovered that I have a pituitary macroadenoma that is being watched.  Is it possible that this is causing the TSH to be so low?  What else might cause this?

Thank you.

[goolarra]

TSH is a pituitary hormone, so I assume any pituitary issue (like your macroadenoma) coiuld very likely be affecting it.  Your FT4 is at the bottom of the range because your pituitary is not sending out it's signal to the thyroid (TSH) to produce T3 and T4.  You should watch your FT3 carefully to see if it follows your FT4 down.  What are you on for thyroid meds?  Has your endo indicated that he wanted to increase your T4 (levothyroxine) dose?  What is your actual TSH number?

[bated]

Thank you for your response.

I have been taking Levoxyl for the duration of my Hashimoto's.  I am now on 112mcg.  My lab results are below.  I currently don't have a regular endocrinologist.  I just saw a pituitary endocrinologist at MD Anderson for treatment of the adenoma.  He is the one that ordered the lab work and I have yet to get his interpretation.  I parted ways with my prior endocrinologist over a disagreement over treatment options for the adenoma.  I will be seeking recommendations for a local endocrinologist for long term follow-up, but in the meantime will be working with the endo at MDA.

Free T4  1.0 ng/dl  (0.9 - 1.8)
TSH  0.08 mcu/ml  (0.50 - 5.50)
Free T3  3.0 pg/ml  (2.0 - 3.5)

[goolarra]

It's all vey interesting and a bit curious.  Your thyroid must have been still fairly productive until you developed the pituitary problem.  With your TSH at 0.08, your pituitary is now asking it for virtually nothing.  That's why your FT4 has fallen into the low end of the range.  Of course, increasing Levoxyl would help that situation.  However, your FT3 is excellent.  You obviously have no trouble converting T4 to T3.  I can't think of a thing to explain that, except that perhaps it hasn't caught up to your other labs yet.  If your FT4 continues to fall, your FT3 will also.

I don't think there's any way around implicating the pituitary in all this.  Sorry I can't be of more help, but I think you're beyond my scope.  I have a pituitary issue also, but it keeps my TSH artificially HIGH.  I'd be very interested to see what your pituitary endo has to say.  Please keep us posted.

[661822]

I have been hypo with Hiro for 9 years, and my levels will never be right as far as I can tell, however I have found that non genaric meds are a huge difference.  I pretty much demand them because it is so obvious when they are generic.  Good luck and hang in there.
J

[Super_sally888]

Hi,

given the pituitary involvement, testing of TSH becomes useless.  You will need to be tested and medicated on the basis of FT3 and FT4.

Will be interested to see your feedback after you've seen the endocrinologist.

I have microadenoma (when it was last looked at) and my TSH is also pretty much non-existent.  My meds are always adjusted on basis of FT3 and 4 now.