What blood test is most important, T4 or T3?

[GMEN1984]

As the title states, I wanted to know which blood test is most important in checking to see if Antithyroid meds are working. Specifically, methimazole

Is it Free T4, Total T3, Free T3?

Also, which one is the first to show change if the meds are working?

Thanks

[gimel]

Sorry, I knew that but in my last reply I reverted to Free T3 which is usually what is tested, not Total T3.  

Yes a thyroidectomy is a quicker, "more permanent" solution.  I don't know what the odds are that with continued use of Methimazole you could achieve remission from the Graves', but the American Thyroid Association says this.  " Unfortunately, a large percentage of patients either do not go into remission or relapse within the 1st year after stopping the antithyroid drugs."

Should you choose to go with a thyroidectomy, be aware that a good thyroid doctor will treat clinically by testing and adjusting Free T4 and Free T3 levels as needed to relieve hypothyroid symptoms.  Symptom relief should be all important, not just test results, and especially not just TSH results, which is how a lot of doctors determine thyroid med dosage.  That does not work.  You can get lots of info and be prepared to be your own best advocate after a thyroidectomy by reading at least the first two pages of the following link, and read more if you want to get into the discussion and scientific evidence for all that is recommended.  

http://www.thyroiduk.org.uk/tuk/TUK_PDFs/diagnosis_and_treatment_of_hypothyroidism_issue_1.pdf

Please keep in touch and let us know how you are doing and we'll be happy to help in any way we can.  

[gimel]

When looking for information about how long it takes for antithyroid meds to become effective, about all I see is "weeks to months".  Since you have been on 5 mg of the Methimazole from Nov through April, and now on 20 mg since then, I would have expected more of an effect.  Your Free T3 has gone down by only 20% and your Free T4 was basically unchanged.  If it were me I would talk with the doctor and mention that after almost 6 weeks on the increased dosage, you have had little to no improvement in your FT4 and FT3, or your many symptoms,  and ask about a dose increase.    Also ask if there is anything he can prescribe that could provide some short term relief while waiting for the Methimazole to become fully effective.  

[GMEN1984]

Thank you gimel for the reply

I wanted to mention that the T3 test was Total T3 and not free T3.

Also, since its been this long, I am contemplating a total thyroidectomy as it seems like a quicker/more "permanent" solution

[gimel]

I am a bit confused about your test results and meds.  Please post both the prior and most current test results and reference ranges shown on the lab reports.  Please also identify the dates for those tests.   Also, what medication and dosage were you taking at the time of the prior report and what is current dosage?  Also, what symptoms do you have?  

[GMEN1984]

April 27th Methimazole @ 5MG

T3, Total Range = 87 - 190 ng/dL. Results = 281 ng/dL

Free Thyroxine  Range =  0.60 - 1.80 ng/dL.  
Results = 2.63 ng/dL

TSH was <0.01 uIU/mL (undetectable)

June 2nd Methimazole @ 20MG

T3, Total Range = 87 - 190 ng/dL. Results = 225 ng/dL

Free Thyroxine  Range =  0.60 - 1.80 ng/dL.  Results = 2.7 ng/dL

TSH was <0.01 uIU/mL (undetectable)

I was diagnosed with graves a year and a half ago.

What I wanted to know was, is the lower Total T3 a sign that the meds are starting to work?

As for the symptoms, it hasnt improved. Im still dealing with

High resting heart rate, tremors, muscle pain/weakness (paint when lightly pressing on my body), throat pain (not sore throat), eye pressure, shortness of breath.

Im thinking that, since my total T3 went down, that the meds have started to work (slowly but surely) and I just need to give it more time to work?

[GMEN1984]

I made a mistake in the dates. The correct info is as follows

Up until April 27th, I was on 5mg. As of April 28th, all the way to june 2nd; I was on 20mg.

From November through April 27th was when I was given 5mg dosage.

[gimel]

I would not recommend selecting only one test.  I would request two of those.  The thyroid gland produces mostly T4 and a little T3.  Most serum T3 is from conversion of T4 at the cellular level.   T3 is the thyroid hormone that is metabolized by all the cells of the body to produce needed energy.  So Free T4 and Free T3 are the important tests.

A Total T3 test is not very useful since it is a measure of all the T3 in the body, most of which is bound to protein and not biologically active.  Only the small portion not bound to protein, thus called Free T3, is biologically active.  

[GMEN1984]

Thank you for the answer.

I asked this question because my doctor had me take a total t3 tsh and Ft4 test.

My last results were not good so meds were increase and my total t3 came back at slightly abnormal but my Free T4 went up 3% (previously 2.63, now 2.7)

Would these numbers indicate the meds are working as they should? Ive not taken any FT3 tests as my endo has never given me a script for that test.

BTW, My symptoms are still bad but its possible that they could improve if I were to continue taking the meds for another 6-8 weeks? Since my Total T3 went significantly down, maybe this is the case?