Thyroid Disorders Community
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Thyroid function blood test ...

Hi all,

I want to ask please, those of you who do take T4 medications before blood tests, do you know whether it can cause the FREE T3 and FREE T4 to rise and still be within normal range but high in the range? I know that it does not affect the TSH, but what about the FREE Ts ??

I really appreciate any exact answer or help any one of you can offer.
4 Responses
Avatar universal
Yes Free T4 and Free T3 values can get affected especially if you are doing blood test without giving sufficient gap like 1 to 2 months before starting T4 dose or changing dose.

For example if you have changed dose recently like T4 50 mcg to 75 mcg and did blood test after just 1 week then chances there you see a high or normal high Free T4. This is also the reason why people experience temporary hyper symptoms when they start medication or change to higher dose etc.
Hi des900,

Thank you very much for your answer, what if you reduce the dose not increasing it ?

What about if you take the dose of the day of the blood test before the blood is drawn? about 2.5 hours before the blood is drawn, can it affect the values of the FREE Ts by increasing their values within normal range?

I am asking because I did a test, the TSH is normal, but my FREE T3/4 are higher than what I know from previous test is proper for me, and I feel some sort of fluttering in my chest and discomfort in my neck !?

Thanks very much,
Completely normal. TSH not change much if you taken thyroid medication on same day while your Free T3 and Free T4 value changes. If you reduce the dose too it might show false high as you are supplying thyroid hormones externally even if the dose is less.
TSH can change as well as the Free T3 and Free T4.  In addition, there are many things that affect TSH besides thyroid hormones and TSH tends to be highest first thing in the morning...  
Hi Barb135,
I read in many places on the web that TSH does not supposed to change, anyway, in the test I mentioned above my TSH did showed a lower value than what I expected and the FREE Ts were higher than the values I expected, strange right ?!

I am thinking of repeating the test.

Thanks Barb,
649848 tn?1534633700
Yes, abyz321... taking your T4 medication the morning of the blood test, prior to the blood draw can affect your labs for that draw.  I just had this happen last week and because of it, I may end up having my dosage dropped, even though I have a few hypo symptoms.

I had gotten up in the morning and taken my T4 med at the usual time, shortly after 6:00 am, and had my endo appointment at 8:20 am.  Because my labs had been drawn several weeks earlier with other labs and there were some disturbing results, unrelated to thyroid, my endo decided she wanted to draw new labs that morning, which I had not expected or I wouldn't have taken my med...

The previous (Dec 5, 2016) results were as follows:  Free T4 = 1.1 (0.8-1.8); Free T3 = 3.3 (2.3-4.2); TSH = < 0.01.  My TSH is always low, which is a constant source of discomfort for my doctors.  Anyway, the new results (Jan 5, 2017) were Free T4 = 1.4; Free T3 = 3.5 and of course, TSH at < 0.01, as usual.  The reference ranges were the same for both draws.  The only difference between the 2 draws was that I'd taken my T4 med prior to the second draw.  I was not aware that it could increase FT3 levels, but apparently, it can...

Because I took my med prior to the blood draw, my FT4 went to 60% of the range vs 30% in Dec and my FT3 went to 63% of the range vs 53% in Dec.  I haven't heard from the doctor yet to see if she's going to lower my med, but I know my TSH was, literally, causing her own heart to flutter...
Hi Barb and des900,

I repeated the TSH, this time early morning before taking that day dose of Levo and the results were 1.3, strange right?

What do you think?

Hi Aby... I'm sorry, I'm not seeing what your actual previous TSH level was, only that it was normal, in spite of reading through your posts a couple of times...

Is TSH the only test you repeated?  Unfortunately, TSH should never be used, alone, to decide whether your dosage is accurate or if your levels are optimal.  TSH is a pituitary hormone, not a thyroid hormone, so it's, basically, only good for helping with diagnostics.  Free T3 and Free T4 should always be tested and used to help determine or whether one is optimal or not...

TSH neither causes, nor alleviates symptoms; levels of Free T4 and Free T3 determine how one will feel.

If you'll post your actual lab results for Free T3, Free T4 and TSH, along with reference ranges, we can help you determine what might be the cause of your symptoms.  It's unlikely that taking T4 medication would cause symptoms to arise that quickly, however, anything is possible with thyroid...
You can know if your current symptoms is from thyroid then simply look at your Free T4 and Free T3. Increased Free T3 can bring huge hyperthyroid symptoms especially increased heat, blood pressure rise, unable to sleep at night etc while increase Free T4 can bring some of the hyper symptoms, for example diarrhea, fast heart rate etc. TSH is a poor marker and its value changes during day. For example on morning its value is least and after noon its value get reduced. So simply look at TSH values will not get the whole picture. Also TSH responds slowly and usually take about 4 weeks to completely settle to suitable values after changing dose so during this period its common to experience some hyper symptoms.
Sorry I mean after noon TSH value tends to raise.
Hi Barb and des,

The TSH from blood draw with that day dose taken was 1.44 and the TSH about ten days later without taking the Levo until after the blood drawn was 1.3 which is strange right? the last test my doctor ordered only TSH since it was only one week after the previous test.

Any ideas ?
I appreciate your help.

I didn't understand are not taking levothyroxine or taking levothyroxine at  some dose? If the TSH of 1.44 or 1.3 is without taking levothyroxine after around 10 days then probably you do not require any levothyroxine medication provided your Free T4 is not below mid range in reference range that's why its very essential to do the Free T4 and Free T3. Free T4 is particularly useful for detecting hypothyrodism and Free T3 for hyperthyrodism.
Hi des,

I have hashi and hypo, I am already on levo, but not feeling well yet, after my dose reduced one day in the week from 150 to 100, the 1.44 is 2.5 hours after taking my dose of levo and the 1.3 is before taking the dose of that day, both were done at 7AM and same dose!

Both 1.44 and 1.3 TSH value is normal and nothing to worry about provided your Free T4 value is normal too preferably in mid range in given reference range. TSH normal value for general population is very broad like .3 to 5 and the reason for that is TSH can fluctuate during day also TSH values of nromal thyroid function people too vary a lot with no symptoms so no need to think much about TSH provided its contained in reference range (excluding conditions which have raised or lowered TSH value like pituitary adenoma, thyroid hormone resistance, pituitary failure etc).
But I am still symptomatic ??!!
Aby, I don't think des900 understood what you were saying, so let's make sure we all understand.

From what I'm understanding, one time you had blood drawn, you took your medication prior to the blood draw, and got a TSH of 1.44.  10 days later when you had blood drawn, you did not take your medication prior to the blood draw and got a TSH of 1.3... I'm also understanding that you "do" take thyroid hormone medication on a daily basis...is my understanding correct?

What I'm trying to tell you is that TSH tends to be highest first thing in the morning and gets lower as the day goes on. However, TSH is variable and is affected by a lot of things.  In addition, TSH neither causes nor alleviates symptoms, so your TSH value is irrelevant, whether it's in range or not (my own TSH stays at < 0.01 all the time).  What we're really concerned with are your Free T3 and Free T4 results and their reference ranges.
Hi Barb,

Yes, your understand is correct.

I know that TSH can change intraday, the two tests were at about 7AM.

My Free T4 is in the upper half and FREE T3 in mid range, however compared to previous tests, FREE T3 is higher than were I feel good ( I feel comfortable with FREE T3 low in the range).

Hi aby... Is there some reason you don't want to post your actual Free T4 and Free T3 results with reference ranges?  Just telling us that they're in the normal range or that Free T4 is in the upper half, etc is not very helpful.
I did want to add that your aren't required to post further labs; it's just that there's only so much we can tell you, without them...
Hi Barb,

TSH : 1.44   .
FREE T4 : 19  : [12-22].
FREE T3 :  4.7: [3.5-6.5].


These are perfectly fine thyroid results, if you are still having hypothyroid symptoms do check these

CBC (to rule out anemia)
Vitamin D (25-hydroxy Vitamin D)
Vitamin B12

After testing please post the results with given reference range as values need to be in optimal range and not just normal.
649848 tn?1534633700
These are not perfectly "fine" thyroid results, obviously, because you don't feel fine... Your Free T4 is at 70% of the range, when it's recommended that Free T4 be maintained at around mid range.  At the same time, your Free T3 is only at 40% of its range, when it should be in the upper half to upper third of its range.  You should maintain a balance between Free T4 and Free T3 and yours is upside down;  Free T3 should be higher in its range than Free T4 in its range.  This imbalance between Free T4 and Free T3 can cause the symptoms you're having.

It would appear that you might not be converting the Free T4 to Free T3 adequately.  Typically, when Free T4 is too high and Free T3 is too low, the protocol would be to decrease T4 medication and add a small amount of T3 medication, such as Cytomel or its generic counterpart, liothyronine.
Hi Barb,

With those results I feel slightly hyper, and I feel comfortable with FREE T3 low in the range !

Those results are fine no need to worry much about it though 50% Free T4 and 75% Free T3 ideal situation there but its like needless perfectionism and Free T4 and Free T3 values can vary and not fixed entities also adding T3 medication is not safe as you are already experiencing hyper symptoms though your test results not reflect it, may be due to other problems like adrenal problems, anxiety issues, heart issues etc. If you are having symptoms do the other tests said and make sure its in optimal range.
Hi des,

Cortisol was normal so are B12 and vitamin D .

Ferritin and CBC as well.

Please post the actual results with reference range as normal ranges are very broad while optimal ranges are usually narrow. For example B12 normal level in between 200 to 900 while optimum level above 500. For Vitamin D normal value between 30 to 100 while optimum 50 to 70 thus this is a huge difference between normal and optimum and you need to remain in optimum levels.

Also do include zinc and selenium rich foods in your diet as it helps in T4 to T3  conversion. Zinc is needed daily as body not tend to store it so deficiency in it can create problems.
Dear des,

B12>500  .
Vitamin D optimal  .

649848 tn?1534633700
Aby, I'm not worried about needless perfections, but I'm not here to argue the point and I'm going to back out of this conversation.  I'll just leave you with a couple of things to think about... First off, having Free T4 that's too high, can also cause hyper symptoms.  Some symptoms, such as heart palpitation, rapid heart rate, the chest "flurries" and throat issues you mentioned can "cross over" and apply to both hypo and hyper.  

Please understand that just because a result is in the "normal" range, it's not necessarily "fine"...

I wish you the best of luck...
Thank you Barb135 and thanks for the time you devoted !

Best of luck to you too,
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