Question about diagnostic value of total t4 (and unfortunately a lot of rambling)

I assume people have nothing better to do on Friday night so I am asking does TT4 matter? And what does it mean?

No need to go into details explaining the difference of ft4 and TT4, no offense, but I am fully aware of that. I am asking this because I happen to have both low, but most doctors haven't even heard about TT4 and over here in Finland it is rarely measured, couldn't find any laboratory that would measure it.

I have had it done through ZRT lab, not requested, but it has been a part of complete thyroid panel.

I have no other illnesses, at least based on test results, healthy kidneys, healthy liver, no inflammation, I am not on ANY medication, I do not even use pain killers, all I take is vitamins and nutrients. My test results are not affected by any of things mentioned above. Of other possible factors I am not aware, so far I am considered otherwise healthy. Only mildly deficient to iron , my serum iron and ferritin are a bit below optimal range so not sure if that would have such a dramatic effect. Besides when I have been reading a bit about iron I have understood its much more complicated thing and our bodies have the ability to down regulate iron in order to protect us as many pathogens consume iron, so during illness our system does whatever it can to protect from more harm. Maybe more about that in another posting.

My total t4 and ft4 both have been dropping.

2014 TT4 6 (5-10.8) Ft4 1.6 (0.7-2.5)

2015 TT4 4.8 ft4 1.2

2016 TT4 2.5 ft4 0.9

I am not asking for help with numbers per se, just demonstrating random tests, and in this case they are mine.

Question is has it any relevance generally speaking? See the chart how to interpret thyroid blood tests ,TT4 has relevance.

I googled some and found some interesting research. In China they suggest TT4 over ft4 because of the unreliability of ft4 measurement. Not suggesting they are right, but they are not that much wrong either as ft4 measuring can be very unreliable and in uncertain cases it should be tested with different method and in different laboratory too, which to be honest, I rarely see done. Ofc high TSH, antibodies present etc gives in hypothyroidism, so its not always necessary to question the ft4 test result except if doctor solely relies on TSH and ft4 adjusting thyroid medication and ignores how the patient is feeling.

I see very different combinations of TT4 and ft4, but thats partially down to different factors, ie other illnesses, medications, contraceptive pills etc I assume?

So has it any diagnostic value and how one should look at it? I know in case of severe NTI low TT4 might not indicate anything good, when it drops below certain level it predicts 80% higher mortality. This is a question I have asked from doctors and they keep staring at me and do not know what to say. So if I am not severely ill and about to drop dead in near future it has to mean something, otherwise I suggest they should hospitalize me ASAP! :D

2 Replies

  • If FT4 can be measured, TT4 is redundant .Because TT4 measures everything of that hormone in your blood. the large amount stuck onto transporting proteins and the little free fraction. The problem is that people have different amounts of proteins that bind T4 as a reservoir, so that the same FT4 can be obtained from such different reservoirs containing different amounts of T4. You can work this out by a simple formula but I won't go into that here.

  • Not to answer your question, but the Blue Horizon bundles of thyroid tests often include TT4. When the owner was on the forum he said the lab does it as part of the process, so it costs no extra.

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