Thyroid Function Tests, What Do They Really Tell Us

The TFTs, (TSH, T4, T3, FT4, FT3, Tg,) are useful only if you understand their limitations. There are four areas that are problematic.

The first is that until very recently there has been no attempt at a unified standard. Each lab sets their own reference range either from the vendors calibration kit or from establishing a reference range based on a minimum of 120 highly qualified subjects. This means that if you sent a single serum sample to 10 different labs you would get 10 different results with 10 different reference ranges. If you ran a single serum sample on 20 different vendors equipment you would get 20 different results with 20 different reference ranges. You also have the problem that the different chemicals used by the different vendors will react differently to some of the TSH isoforms. In 2007 The IFCC, International Federation of Clinical Chemists, established a committee to 'harmonize' the TFTs so the results from various labs and vendors will be within plus or minus 5%. This is still a work in progress. The FT3 test had a variance of up to 60% so that is going to take some work.

The second problem has to do with the reference ranges, most notably with the TSH. In 2002 the NACB, National Academy of Clinical Biochemists, said that in the future the top of the TSH should be 2.5. In 2002 AACE, American Association of Clinical Endocrinologists, suggested a RR of 0.3-3.0 because the TPO and TG AB tests start showing results around 3.0. That started the TSH reference range wars which Mary Shomon has written about. Today in the US most RRs run from 0.1-0.5 on the bottom and 4.0-6.0 on the top.

The third, and perhaps the most critical, problem is the 'low index of individuality'. Each of us has our own individual reference range which is actually fairly narrow, about plus or minus 1.0 from our own mean. Also, all of us have slightly different set points in our bodies for TSH, T4 and T3. We do not all share the exact same set point, it varies for each individual. This means the TFTs cannot tell you where you are in regards to your own personal reference range and set point. They can only tell you how you relate to the broad range of a group of people. This is very a important concept to understand. The reference range is the broad side of a barn. Somewhere on that broad side is a door large enough to drive a tractor in. The door is your own personal reference range. Where it is on the side of the barn varies from barn to barn. The TFTs only know the broad side of the barn, they have no idea where the door is.

The laboratory reference range is not the patient's reference range.

As Dr. David Derry said, "The TSH had a ring of scientific rigor for those who have a smattering of knowledge about thyroid metabolism. It was part of the pituitary feed back mechanism for monitoring the output of the thyroid gland. There is no doubt that it does accomplish this job. But unfortunately the TSH value has no clinical correlation except at absolute extremes with the clinical signs or symptoms of the patient."

Lastly, most allopathic doctors treat the TFTs as absolute and infallible, if your results are in the reference range it can't be a thyroid problem, period. Unfortunately, there are several problems that the TFTs can miss completely such as conversion problems, thyroid hormone resistance or the early stages of Hashimotos. This results in an inferior standard of treatment that leaves many of us sick, or makes us sicker, or destroys our relationships with our loved ones, or destroys our careers, or destroys our lives.

There is more to it than that but this is a simplified outline. I have included a link to a good presentation, about 18 minutes. You want "TSH Reference Range Redefined" by Dr. Lee. This will not work on a Mac, only on a PC. PR

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32 Replies

  • Thank you PR4NOW - that has helped me to help others..... it will be filed in a safe place !

  • Marz, I had to correct a couple of typos and add a couple of bits. PR

  • Hi,

    Apologies if this is a silly question, I should probably know better after over 20 years of thyroid issues, but although on meds I still have issues and your post seemed so knowledgeable I thought I could ask you for clarification?

    I started hypothyroidism with high levels of TSH, wheich then eventually went down to negligable - doc said this was because my body makes TSH to get the thyroid to produce thyroxine and I was not so it made lots and eventually gave up

    I have been taking Thyroxine for about 17 years as levothyroxine, and I looked this up and my understanding is that this replaces the T4

    I have also looked up the condition ( mainly to see why I am still feeling so many hypo effects on 150ug a day) and I came accross T3, which the doc had mentioned in passing but no idea why it is different to T4?

    I have no idea what the other acronyms you mention mean.

    I have a TFT test ( blood test) every 6 months now, but I never see the results, if I want to know the results I have to call the docs and then the receptionist tells me it is within expected ranges - but no idea if that means it is good, or just good enough for me? or if this test covers the T3

    The reason I am so interested is that I am so tired all the time - I sleep through most weekends ( about 16 hours but if I can get away with it - i.e. holidays with no washing to do, dinner to cook etc, I have been known to sleep through 3 days - only getting up to go to loo, blearily downing some water and then off to sleep again)

    If you have any answers or links to any info relating to my queries that I might understand I would appreciate it greatly, as am building myself up to having another discussion with the docs about this ( they are a bit dismissive and I find it hard asking them questions so have to prepare myself)



  • In writing ask for a print out of all your results to date and doc can do it and then you can pick up from doc reception the letter. Or ask for a print out in an appointment. Say it is for your own personal records. This is what I do.

  • There is absolutely NO need to provide any reason whatsoever for wanting a copy.

    (This is not meant to criticise you at all. Just that doctors have no right to ask for or expect any justification.)


  • yeah I was just saying what I do. Sometimes they say why (they dont always ask why) and it shuts them up is all....

    they go no problem and all is fine. Some people feel good knowing how to respond if they arent the most confident folk.

  • Understand - I get upset when patients are made to feel they have to provide an answer - but if it is their (or your) way of deflecting things, then that is fine - and may well be helpful. :-)

  • :)

  • Hi, I got the results from my doctors - posted them somethere on here, but as far asa I can see I am outside the "normal" ranges for every test other than 3, and htat is over nearly 15 years so not sure why the surgery tells me they are within expected ranges?

  • Fair comment.

    These medical records BELONG TO PATIENTS, not to doctors.

    As always, doctors use their power to intimidate patients.

  • Absolutely - now. Time was, however, they were regarded as doctors' property. Some doctors continue to treat them as if they were.

  • Hi Omega,

    I am hoping my docs will be happy to provide the info, I have not asked them so far ( tricky to get past receptionist, so they have not refused to give it to me) and as Anuba says, I am not confident in these things, I think it is because when I have asked them about things I dont understand in the past they have gotten a bit testy with me, it is probably because they only have 5 minutes per patient and as I am just asking for info, they probably feel their time is better spent with someone really ill - which I can understand.

    They are very busy at our deurgery, the doctors waiting room is always full - I think they cover a large geographical area, and you need to call each moring for about 10 days before you can get an appointment if it is not urgent, although I have noticed that if you go to the receptionist and tell them the doctor has asked to see you again ( after an appointment) they can ususally book you in within a week.

    So I assume the docs are just a bit overworked, which does make me nervous in asking for the info - I do not want them to think me too demanding, I need them to be motivated to help sort out my current issues and not just mark me down as an irritating patient.

  • Just clicked on your link , Rod, and it took me into something very suspect - definitely NOT an NHS page - just thought I should mention it as I had to fiddle about and shut my computer down to get out of it.

  • I have checked and re-checked - something odd is happening to you but not to me!

    It could be some malware on your computer (or whatever device you are using), or the way you are connecting to the internet.

    Or it could be how your browser is mis-handling the links- especially when they wrap.

    Try this:


  • Think I have found the answer:


    So glad it wasn't me after all! :-) :-)

  • Hi Rod

    didn't think it was you, just that something odd was happening and others might get further into it without realising. I'm impressed that you got to the root of it!

    The link is working fine now. :)

  • Don't worry - I didn't take it personally! And I agree about warning others - definitely a good idea - thanks.

    But it could have been a mistake - I certainly find things not quite right in some of my posts months or years old. :-)

  • At least most of the acronyms used above and, indeed, in most posts here are contained in my document here:

    Hope this helps.


  • Mrs_Somerset, you are not adequately treated! The doctors in the UK tend to treat the lab test and ignore the patient and their signs and symptoms. Please get copies of your lab tests and post here for comments and always get copies for your own file. It is possible you have a conversion problem converting T4 to T3 or a DIO2 defect. T4 is a pro-hormone that needs to be converted to T3 which is the biologically active hormone used in all the cells. You have to fight like heck to get adequate treatment. PR

  • Hi PR,

    Thank-you for the advice, I have seen others post their results here seeking advice, as soon as I have summed up the ocurage to ask for my results I think Iw ill post them here - you guys know so much and might be able to clarify for me why I feel so rotten.

    I have got other issues at the moment - I injured myself in September and this has lead to other issues whic I would really like the docs to sort out as a matter of priority and then challenge them about my thyroid, although I am starting to suspect some of the issues I currenly have are being made worse if I am low on vit D, vit B12 and thyroid imbalnces.

    I am feeling more able to ask the questions that need asking thanks to the support from others here - it is so helpful to hear from others with similar issues, makes me feel less alone and less foolish.


  • Mrs_Somerset, you are not alone and you are not foolish. As you feel up to it you are welcome to participate, ask questions and learn. This is what we all have to do to get our lives and health back. PR

  • Good precis of current position. Here is a brand new good source of bedtime reading on T4 (and mixed) therapy - 80 pages long, so keep at least a day free

    Endocrine Reviews

    Treatment With Thyroid Hormone

    Bernadette Biondi and Leonard Wartofsky


    Received: July 27, 2013

    Accepted: December 03, 2013

    Published Online: January 16, 2014

  • Unfortunately, seems to be behind a paywall. :-(

    I'd love to read it.

  • Hi helvella

    Many thanks for your insights as before!

    I was wondering if any of us can obtain a pass to a local university library for free access to these articles? I might find out myself.

    I used to go to British Library (London) when I happened to be staying in London a few years ago.

    Best Rgds,

  • Diogenes, I am especially interested in two areas, testing and the one we talked about a few days ago which very well may influence testing problems. I'm working on writing a long form piece about testing which will be fully annotated and referenced. This was an attempt to put some of that in the short form format you need to post on a forum. I have a favor to ask. When I finish the piece would you read and critique it. I need someone with your training and caliber of mind to play 'devils advocate' and point out the flaws in my thinking. I want this to be a solid piece of writing that can withstand any onslaught of criticism. I intend to post it on as many thyroid patient sites as possible. Patients need to understand the standard of treatment they are being subjected to, it is the only way we can learn to survive it. PR

  • OK, send it along and I'll see what I can do. You have my mail address.

  • Diogenes, it will be another 2 months or so before it is finished. Thank you, PR

  • I tried to get it through my uni access but I can't get it yet as it's only 'early access'. Can get this one though by the same authors. But maybe everyone else can anyway.

    Combination Treatment with T-4 and T-3: Toward Personalized Replacement Therapy in Hypothyroidism?

  • Thanks for trying.

  • From the website - so should be available soonish

    Early Release articles are PDF versions of manuscripts that have been peer reviewed and accepted but not yet copyedited. The manuscripts are published online as soon as possible after acceptance and before the copyedited, typeset articles are published. They are posted "as is" (i.e., as submitted by the authors at the modification stage), and do not reflect editorial changes. No corrections/changes to the PDF manuscripts are accepted. Accordingly, there likely will be differences between the Early Release manuscripts and the final, typeset articles. The manuscripts remain listed on the Early Release page until the final, typeset articles are posted. At that point, the manuscripts are removed from the Early Release page.

  • Hi

    Another question is, it's good that we stay educated re. thyroidology.

    But would hospital consultants take heed of information/articles we (patients) present to them? In my previous experience, it's a slow process if not impossible.

    Consultants generally seem to pick what they want to believe or pick what they were told by their colleagues at hospital. Sometimes, their belief system is outdated and wrong (sadly, quite commonly) whilst we (patients) know better.

  • Thank you! That's really interesting. Fortunately I have a very approachable doctor who is willing to listen to me.

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