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Avatar universal

What could be causing low TSH but normal T3 and T4?

I have been taking 100 mcg of Synthroid for about 10 years for hypothyroidism.  My current lab tests show TSH is 0.24 (reference range 0.40 - 4.50 mIU/L); T4, Free is 1.5 and T3, Free is 2.9.  My doctor ran these labs after I began having symptoms of leg muscle pain and weakness, occasional heart palpitations, periods of fatigue, anxiety, being very emotional and having trouble sleeping.  I notice that my temperature runs about 1-2 degrees below normal, but have occasional hot flashes.  My hands are often cold.  I am quite overweight and have NOT lost weight recently.

The doctor is having me do a thryoid ultrasound, and referring me to an endocrinologist.  Has anyone out there had experience with low TSH/normal T3 & T4, and what was the outcome?  Thank you
4 Responses
Avatar universal
There are scientific studies that show TSH suppression frequently occurs when taking adequate thyroid medication.  That does not mean hyperthyroidism, unless there are hyper symptoms due to excessive levels of Free T4 and  Free T3, which is not the case for you.  I have more info for you if you will first post the reference ranges for the Free T4 and Free T3tests, as shown on the lab report.    
Thank you, gimel.  Free T4 reference ranges are 0.8 - 1.8 ng/dL, and Free T3 are 2.3 - 4.2 pg/mL.  I am female, in my early 60's.
Avatar universal
In assessing a person's thyroid status, the most important consideration is symptoms, followed by Free T4 and Free T3 levels compared to their reference ranges, plus other variables.   You have numerous symptoms that are frequently related to being hypothyroid.  Your Free T4 is at 70% of its range but your Free T3 is only at 32% of its range.   Just because both are within range, does not mean that is optimal for you.   A good thyroid doctor will treat a hypothyroid patient clinically by testing and adjusting Free T4 and Free T3 as needed to relieve symptoms, without being influenced by resultant TSH levels.  Symptom relief should be all important, not just test results, and especially not TSH results when already taking thyroid medication.  Many of us have found that we needed Free T4 at mid-range, at least, and Free T3 in the upper third of its range, and adjusted from there as required to relieve hypo symptoms.

In addition take note that  hypothyroidism is not just inadequate thyroid hormone.  Hypothyroidism is best defined as insufficient T3 effect in tissue throughout the body, due to inadequate supply or, or response to, thyroid hormone.  So it is the extent of Tissue T3 Effect which determines your thyroid status as either hypothyroid, euthyroid, or hyperthyroid.  

When taking T4 type med like Synthroid, it is very common for FT4 to be higher in range than FT3, due to inadequate conversion of the T4 med to T3.  There are several variables that can affect conversion, including ferritin as one of the most important.  In addition, serum levels of thyroid hormone may not accurately reflect tissue thyroid levels because of the many variables that affect transport of thyroid hormone into tissue.  Also, thyroid hormone at the tissue level is affected by several variables, including cortisol and Vitamin D.  I am relating all this to make clear that the typical standard of care from most doctors, based mainly on TSH for both diagnosis and treatment, is insufficient.  You can confirm what I have said by reading at least the first two pages of the following link, and more if you want to get into the discussion and scientific evidence for all that is recommended.  


So, I suggest that you need to get some additional tests done.  In Sugg. 4 on page 2 of the link you can note that you should always test for both Free T4 and Free T3 every time you go in for tests.  In addition, it would be good to test for Reverse T3 at least once to determine your Free T3 to Reverse T3 ratio.   RT3 is a normal product of conversion of T4, but under some conditions an excess is produced which adversely affects tissue metabolism of Free T3.  In addition, low or high cortisol can also cause problems.  Your body requires adequate cortisol, but it is an antagonist of thyroid, so an excess is undesirable.   Two other important tests for hypothyroid patients are Vitamin D and B12.  So you really need to request to be tested for Reverse T3 (and a Free T3 from the same blood draw).  Also request a test for cortisol, Vitamin D, B12 and ferritin.  With the D, B12 and ferritin tests in hand you can supplement as needed to optimize.  D should be at least 50 ng/mL, B12 in the upper end of its range and ferritin should be at least 100.  After correcting any deficiency in D, B12 and ferritin,  I think it is likely that you will still need to request that the doctor add a source of T3 to your med to raise your Free T3 level.  Along with that he could slightly reduce your T4 dosage to get your Free T4 to mid-range.    

You can find all this in the link above, so if your doctor resists doing these tests and treating you clinically, as described above, then you will need to find a good thyroid doctor that will do so.  

Gimel, thank you for all that comprehensive information!  I have started to read the attached PDF, and hope to understand it.  Along with my other symptoms, I find it hard to concentrate now.  I'm feeling pretty bad, and unfortunately cannot get an appointment with the endocrinologist until the end of this month.  

I am anxious to get his diagnosis and treatment, and know how important it is to get a GOOD doctor who is open to running the tests you mentioned.  I do know at least that my B12 is more than adequate according to my labs (1674), because I take a supplement.  My Vitamin D is 43, so I guess I need to take more of the D3.  I think my cortisol must be running high lately, as I feel so stressed and have a greatly increased appetite (NOT good).  
Avatar universal
Based on the experience of many people I would not have great hopes that the Endo will be a good thyroid doctor that will treat you clinically, by testing and adjusting Free T4 and Free T3 as needed to relieve hypo symptoms.   Most Endos diagnose and treat a hypothyroid patient based primarily on TSH, and sometimes Free T4.  That is inadequate.  

Why did your doctor feel the need to refer you to an Endo?  Your doctor could do what you need, if he is wiling to pay attention to symptoms and adjust your med as needed to relieve symptoms, and prescribe T3 med if needed.  Do you think you could give him information and persuade him to do that?  If so, I have some additional good info you could use.
Sorry for the late response--I'm in the process of moving.  Yes, I have heard that about some Endos, and don't understand that at all because they're supposed to be specialists!  How can they not know all about the thyroid?  

To answer your question, at the time I was having these symptoms I couldn't get into my primary family doctor, so used an Urgent Care.  The P.A. there referred me to the Endo after getting the labs back.  I don't know if my regular doctor would adjust my meds according to symptoms, or if he will just leave it up to the specialist.  I will see what happens after the visit to the Endo.  Fingers crossed!
Well, I finally saw the Endo.  According to the ultrasound, the conclusion is that I have a "1.8 cm hypoechoic left thyroid mass with a few central calcifications; a 9 mm nodule is at the inferior pole of the thyroid".  He is scheduling me for a biopsy.  The Endo also lowered my dose of Synthroid to 88 mcg.  

When I saw my GP, he said that 1) the nodule(s) do not affect thyroid function 2) he doesn't think my symptoms are caused by my thyroid and 3) he thinks I should stay on the 100 mcg dose of Synthroid.  He is increasing my Progesterone to 200 mg. daily instead of 100 mg., because he thinks that may help.  I am really confused now.  I'm not sure which dosage of Synthroid to take, and I think my thyroid is the cause.  
Avatar universal
Endocrinologists  are the accountants of the medical world and some are pretty crummy at numbers.
I'm sure hoping I get a good "accountant" then :)
I fired 2 of my accountants ......those 2 were breaking my bank.
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