Thyroid UK
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Are Total T4 and T3 tests any use? Or just Free T4 and T3?

I'm going to a meeting with my CCG soon, and am asking questions about thyroid testing as well as thyroid medication.

If we could choose which tests are the most useful for NHS to provide, which would they be?

So far I'm thinking FT4, FT3, TSH, Antibodies. Should I suggest Total T4 and Total T3 too?

RT3 would be good, but can you imagine NHS doing that?!

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I'd ask diogenes for his learned opinion.

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Oh yes, thanks...

diogenes would you be able to give a short explanation please?

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I would just ask for TSH, fT3, fT4. I think antibodies are useful if patients have symptoms with normal hormone levels or if their blood test results are jumping around. I think total T3 and total T4 are only useful in rare cases where they need to measure the output of the thyroid. Similarly, I don't see much use for rT3, I don't think anyone can relate specific values of rT3 to symptoms or underlying causes.

The following may be useful. I submitted a FOI request to my local health authority regarding the cost of running the assays. This is just the cost of the assay, it doesn't cover the cost of taking the blood or having a follow up appointment.

TSH cost £0.90

fT3 £0.92

fT4 £0.92

These costs are set whether they are combined or ordered separately, just added together as per order. We trust this is now complete and thank you for your interest in London North West Healthcare NHS Trust

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That's interesting. The fact they won't do fT3 made me think it was more expensive.

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They get mixed up. As the thyroid starts to fail TSH rises and fT4 falls but initially fT3 stays the same. Thus, fT3 is not much use for early diagnosis of primary hypothyroidism. However, it is very useful for monitoring the progress of treatment, especially in patients who are not responding well to medication.

We have been mislead regarding the cost which is nothing compared to the cost of extra visits to the doctor and prescriptioins for things that do not work.

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There is an explanation of why FT4 and FT3 testing is important within this link.

thyroiduk.org.uk/tuk/testin...

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Some of this is a little inaccurate. The quoted fT3 reference interval is a little unusual, the most common one is 3.5 - 6.5. Relative fT3 / fT4 levels can give a clue to conversion provided there is enough fT4 and not too much (type-1 deiodinase takes over). The comment 'and high if you have blocked receptor cells' is silly, only a tiny fraction of T3 actually binds to receptors.

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I shall refer your comment to TUK.

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This document on our website needs updating which we will do for the new website. The ranges have changed over the years and are lower now.

In respect of the "blocked" cells, I think it probably refers to thyroid hormone resistance which gives normal TSH and high FT4 and FT3 - endocrinologyadvisor.com/en...

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Mutations of TRB1/2 receptors presents with elevated fT3 or fT4 and non-suppressed TSH. In this case there is a similar level of receptor binding but some of the receptors are mutated thus producing a form of resistance to thyroid hormone (RTH). It makes sense to review it with the new website as the science has moved on since the original article was written.

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As far as thyroid function tests direct are concerned, TSH, FT4 and FT3 will suffice. But their use must be put in context. TSH is best for primary diagnosis of hypo and hyperthyroidism. It is not good for controlling thyroid hormone treatment. FT4 is useful as a confirmation of hypothyroidism and FT3 confirmation of hyperthyroidism. FT4 in thyroid hormone therapy is only useful if there is suspicion of noncompliance in taking the pills - high TSH and low FT4 will result. FT3 is valuable in assessing control of thyroid hormone treatment but should be posponed if there is suspicion of accompanying and debilitating nonthyroidal illness. It is of no use in hypothyroidism.

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"FT4 in thyroid hormone therapy is only useful if there is suspicion of noncompliance in taking the pills" sounds like blaming the patient for undermedication, which would surely have the same result.

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Unfortunately, noncompliance is a frequently found situation. It can be diagnosed by: 1) if the patient hasn't taken therapy for a while, then TSH will be high and say FT4 low. 2) if the patient remembers just before going to the doctor for testing, then TSH will be high and FT4 normal. Not all patients are responsible about taking their medication faithfully as requested. Suspicion of noncompliance usually comes after several tests over the past have shown normality and the new test shows the tablets haven't been taken for a while.

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Hmm. On here,. we usually hear of that being said to undermedicated patients who have been taking their levo but have high TSH and low free T4 - because their dose is too low. Surely, it's possible that (esp with autoimmune attacks), 50mcg might give "normal" results to begin with but then be too little as the thyroid is destroyed. I can't comment personally as I have central hypo and my TSH never does much whether I take meds or not.

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So then which test is useful in controlling treatment in Hypothyroidism...?

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FT3 first, and FT4 only to confirm compliance taking pills, TSH not.

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diogenes Can you clarify 'It is of no use in hypothyroidism', I think you are referring to diagnosis of hypothyroidism as opposed to titrating treatment but this sentence is not clear.

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I mean that FT3 values measured in untreated hypothyroidism are not diagnostic, and I am making no reference to T4 combination or T3 treatment. This is a separate issue

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Diogenes, but in treated hypothyroidism FT4 + FT3 can be used to look at the ratio to see if a person is converting, correct? In treatment a low FT3 would not be good if accompanied by the signs and symptoms of inadequate FT3? PR

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In under treatment where TSH is high, the FT4/FT3 ratio is not so indicative of conversion, because with the lowered FT4 level, the enzymes can more efficiently deal with this to convert to FT3 so the ratio is misleadingly lower. It's only when one gets into the situation where so much T4 is being given to normalise or repress TSH that the enzymes, if they are inadequate, get overwhelmed by the T4 substrate and cannot make enough T3 then start to make some rT3 instead. The situation in untreated "hypo" state is fundamentally different from the "attempted successful state"

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Yes confused me as well!

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