Thyroid Tests: Confusion reigns!

For me as a working scientist, this forum is a rich source of data regarding the normal ranges that different hospitals use for TSH, FT4 and FT3. And what utter confusion there is! Perhaps TSH ranges are somewhat more harmonious, but only somewhat. The quoted FT4 and FT3 ranges however are enormously variable from source to source. For FT4 you might have the lower limit anywhere from 7 to 10 and the upper limit 18 -25. FT3 lower limit 3 - 4.5 and upper 5.5 - 7.5. Since the human race is exactly that and doesn't significantly differ from place to place, differences of 30-40% in range limits for FT3 and 25% for FT4 simply is unacceptable. How patients moving from one hospital's tests to another's get sensible answers is quite beyond me. This has been a rant of mine for 30 years +, that the thyroid profession is complacent and truly ignorant about the tests it so mechanically relies on. Until some degree of rationalisation and consistency is brought about, no wonder misdiagnosis is as prevalent as it is, let alone the basic misunderstandings about ranges in therapy. Goalpost thinking when using range limits simply adds to the confusion. However, this forum's information is extremely useful in gathering experience of these range variations together and I can use the info very usefully in other forums.

21 Replies

  • Diogenes,

    I'm glad that the forum is helpful to you in gathering the vast variation in ranges. Nice to know we're helping you help us :) It would simplify things if ranges were universal.

  • Another thing I find confusion on is that once treated, there seem to be varying opinions on which measurements are useful or valid. I'm T3 treated and the endo measures TSH, T3 and T4 from this he takes note of TSH and FT3 but ignores T4. When I was T4 treated the GP only ever measured TSH and used that alone to dictate dose.

  • Yes, I agree that this is interesting. I think GPs have a range of training, too, and handle the numbers quite differently.

  • Range here in Crete for FT3 is 3.50 - 8.30 - but I presume it is only UK levels you are interested in ....

  • Even that I think is too wide. The range should not be bigger than a factor of 2 e.g. 4-8, or 3.6-7.2 but 8.3 I think is significantly too high.

  • Does that mean that my last FT3 result back in March at 4.28 was better than I at first thought/believed ? Have struggled to increase my dose beyond 50 mcg a day to improve matters. I am T3 only.

  • Look at it this way. The range quoted is 4.8 units wide. Your number goes 0.78 or 17% of the way from the bottom to the top. That's not very high at all but if the range is too wide, then your percentage up the scale will be accordingly higher.

  • I am struggling to understand ! So where would it be better for a result to be ? Have tried various permutations on my calculator to reach the same figures as you. You probably realise I am not a numbers gal .....

    If the range is bigger/wider I cannot understand why the percentage will be higher. Oh dear ....

  • Let's suppose the true range is 3.5 to say 7.0. That's a spread of 3.5 units. You are 0.78 units up from the bottom. Therefore you are 0.78/3.5 = 22% up from the bottom value. That's still fairly low in the range.

  • I have recently been attending some chronic fatigue support groups. Several people I've met have been passed back and forth from rheumatology, to infectious medicine, to neurology, etc, etc. And most have had large batteries of tests and many things ruler out, MRI scans and all sorts.

    I found this a big contrast with my experience as a thyroidectomy patient. Once it was clear Levothyroxine wasn't working for me, I expected that i would be handed on to the next level of diagnostics, and that there would be lots of tests and new theories about what was wrong. But actually I just got shrugged shoulders and "Well, this is all we do, and we've done it all now. You can just go home and manage as you are".

  • The lack of compassion in hyothyroidism treatment makes me almost speechless with rage. Almost.

  • Yea, I thought it would be the same or worse for CFS, but one guy there was saying a few doctors had told him "We know Theres something wrong w you, and in 10 or 20 years we'll be able to identify it", and was being taken seriously by neurologists and having some kind of treatment right now.

    I was pretty gobsmacked. For thyroid they're more likely to say "We know there isn't something wrong with you".

  • Only "almost" speechless humanbean - I find I am frequently seething. My " stroppy socks " getting frequent airing 😈. And to think I used to be a placid little Libran !!! 🙈

  • I was being a little bit sarcastic. :D There are days when I never shut up!

  • This is also one of my bugbears. Thyroid testing is so haphazard. Wouldn't it be useful to us to have a machine like a Glucometer that measures our FT3, so we wouldn't be so reliant on expensive blood tests! It is so good to have your input diogenes.

  • I have long thought it pretty dreadful that so much information is hidden. For example:

    Pathology Harmony

    Pathology Harmony is an initiative working towards harmonisation in UK pathology laboratories which was established in January 2007.

    Although some information is available there, there is little that has changed for FIVE years. And no discussion or background is visible. Has it been abandoned?

    Perhaps they would like a new user/member, diogenes?

  • There is a way forward but it's not infallible. That is to express FT4, FT3 and TSH results not just as numbers but also like I did above express them as percentages up the scale (0 being the bottom of the scale and 100 being the top. This way at least there is some "normalisation" of the various ranges, though of course undue spreads like Marz's report does confuse the situation still to a certain extent.

  • Hi Diogenes

    I thought that the different ranges were due to machine calibration rather than being absolutes. Ie one machine would return a result of (say) 2.5 and another machine would return 2.7 given the same sample so the ranges were set accordingly. Is this incorrect? Are they all measuring absolutes rather than relatives? If so the varying ranges are then a huge worry....

    I agree that treatment for thyroid issues is basic because it's perceived as a trivial condition with a one size fits all treatment.

    I moved onto ndt from t4 only a couple of years ago because I have the Dio2 issue. This made a huge difference to my symptoms. However thE two that I've been struggling with (weight and hairless - I gained over 5 stone in total and lost most of the hair on the side of my head plus thinned on top); while improved on ndt (I lost about a stone in the first year of taking it and the hair on the top of my head is thicker plus I have some hair on my eyebrows now) have not been sorted out. I have turned to a functional practitioner as I don't think conventional meds hold all of the answers. I started an elimination diet and will be taking different supplements plus am having further investigations (sibo suspected). 33 days into the elimination diet I am having some issues but I've lost about 10 lbs and the myxoedema on my lower arms had cleared and is better on my upper arms.

    I think that there has to be a patient specific approach to thyroid issues that addresses individual needs; my current GP is fantastic (he diagnosed me because of symptoms and my below range ft3 and ft4 despite my Tsh being around 1.2) but there are, in my opinion, limits to the reach of conventional medicine; particularly given the funding constraints being imposed by the current government on the nhs

  • No what the various answers are doing is to artificially convert a "relative" value into an "absolute" one. That is, for the particular hospital, they look at their 2.7 as an absolute, whereas hospital 2 on the same patient might regard their 2.5 also as an absolute. Obviously there is a true "absolute" value, which might not be either of these. But human nature being what it is, the tendency is to look at what's in front of you as an absolute "real" value rather than something "relative" and proportional to the real value.

  • Oh dear Lord; so the machines are all calibrated the same and the different reference ranges are set according to the vagarities of the results in the local population? That's appalling but explains why so many are struggling to be diagnosed.

    If this is the case then how on earth would they identify any (say) areas where there was a high incidence of thyroid conditions? If there was an environmental or genetic factor to a particular type of thyroid condition then the ranges would potentially be set either higher or lower or wider range for that local population because the standard deviation curve would be shifted.

    When I hear things like this is makes me wonder how far we've really come in medical diagnosis from sacrificing a chicken and examining it's gizzards to determine a diagnosis

  • Worse than that. The machines don't all read the same, AND very often but not always the labs don't use the maufacturers recommended range but devise their own not always by sound methods,The manufacturers are also often sloppy in determining their recommended ranges and don't probe deeply enough in devising them. When I was working in this, we got the ranges from 55 or more different labs, compared them and if they agreed reasonably well, amalgamated them into a strongly supported general range suitable for everyone, That range was robust and could be used as is, but still individual labs insisted on doing their own. Luckily special situations didn't seem to occur to give significant differences in ranges, even comparing for example iodine-rich areas with iodine-deficient where you might expect to see differences.

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