Thyroid UK
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Blood test confusion

Hi there, I'm confused recent blood test results from doctors. In past tests my doctors has always tested for TSH and FT4 - this time he carried out a whole range of tests but did not include the T4 test.

I have some concerns as my docs advise test result normal yet my weight has shot up by almost a stone within 3 months with no reasonable explanation. i also have a lot of joint pain and tenderness in my achilles.

Can someone please explain to me what the importance of FT4 test is and also T3. Looking back through all my tests I have never ever had my T3 tested

5 Replies

Hi, Tweedy. TSH is the signal from the pituitary to the thyroid to produce T4. T4 is an inactive hormonal element that is converted in the body to the active form, T3. A TSH test alone is pretty meaningless; it is the Free T3 that will give the true indicator of how you are. For best advice here, TSH results along with Free T4 and Free T3 (and their ranges) will produce a decent response. You will also see, if you scan the site, that folk will recommend that tests for, Ferritin, Folate, Vit D and Vit B12 accompany any posts as conversion/uptake is comprimised when levels are askew. Your doctor may not want to test T3 - indeed, the lab may not do it even if he does ask for it, but it is crucial! You may have to insist!


In addition to steviecat comment, the reason you need TSH FT4 and FT3 Checking is to see how your converting. And helps to see what's most likely going in, ie are you converting equally or one more than the other. If your hypothyroid if not supplementing with Zinc your most likely rock bottom in that also so need to try and get that tested too.

And as mentioned Inc results with the ranges the lab used...


'are you converting equally or one more than the other'

Sorry, but what does that mean?


It means if your not converting properly then you most likely have an issue that needs addressing could be nutritional or adrenal. Etc without results and ranges we can't help advice wise...


Thank you, I will dig out latest results as was tested for many things including perimenopause. Seems my tests were sent back and filed away until I asked for response


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