Could anyone tell me the benefit of having both TT4 and Free T4 tested please…just looking at differences in tests and prices please?

[Jo5454]

Hi, I won’t repeat the question, just wondering if anyone could give me an idea on this please. Obviously a bit of difference between the pricing of the two tests I’m looking at and not sure how helpful that info could be?

Im not on anything for thyroid, but tsh has been up and down in past so I keep a check. Recent Drs test showed T4 basically had dropped to bottom of range, but tsh lower than usual & was back under 2. I’ve been very unwell due to needing b12 injections back after trying tablets. Now due vit d check, want to see how ferritin is improving as was 37 due to lowering further after another loading dose of b12. So thought I’d do an all round test to check antibodies, etc again.

Many thanks.

[pennyannie]

Hello Jo :

As I understand things, for this forum, we need Free T4 tested - so to know how much we have freely circulating within our body :

[Jo5454 in reply to pennyannie]

Thank you...i believe both tests do ft4, just that one does tt4 too & I wondered if that was any benefit of knowing...thanks

[FallingInReverse in reply to Jo5454]

Total T4 is not useful for dosing decisions. The vast majority of people on this forum do not get or recommend TT4 tested.

There might be someone who would say differently (although actually with this one I’m not sure).

edit

A compete picture of your thyroid health comes from these tests:

1) TSH

2) Free T3

3) Free T4

Plus these vitamins

4) ferritin

5) folate

6) B12

7)Vit D3

****Consistently test all at the same time, around 9 am is best if you can. Fasting before. No biotin for 3-5 days before. Wait a full 6-8 weeks after a dose change ****

These should be tested … really only need once if positive, or over time of continually negative. A positive rules in autoimmune cause, negative is inconclusive as AB’s can fluctuate:

1) TRab

2) TSI

3) TPOab

4) TGab

[Jo5454 in reply to FallingInReverse]

Thank you for your help & time.. I’ve not heard of all of those 4 listed above…how would we test all of those, or where please?

[FallingInReverse in reply to Jo5454]

Regards to where to get them tested - since I am in the US, I can only recall that other UK folks here likely get them through medichecks or similar?

I will also qualify - that yes there are 4 thyroid-related antibodies, but two are most often associated with underactive thyroid/Hashimotos (TPO and TG) and the other two are associated with Graves/overactive thyroid.

So in practice, for those whose symptoms are well clear of an overactivity - usually we see people only getting the TPO and TG.

Attached is one of my favorite graphics that clarifies the different antibodies and what they mean, and especially the overlaps between their interpretation.

ABs

[Jo5454 in reply to FallingInReverse]

Many thanks, I’ll take a look…yes, seems to be those two over here that get tested!

[Buddy195 Administrator]

We advise FT4, FT3 and TSH are tested. If you have had thyroid antibodies tested in the past there is no need to retest. Also advise ferritin, folate, Vit D and B12 as these vitamins support thyroid health. Medichecks and Blue Horizon are popular companies offering thyroid bloods plus key vitamins.

[Jo5454 in reply to Buddy195]

Thanks…I thought thyroid antibodies can go up and down, or do you mean if I’ve had them tested and positive in past, not to bother again? They’ve always been negative to date….

[Buddy195 Administrator in reply to Jo5454]

If positive previously, this confirms an auto immune thyroid condition, so little point in testing again.

[DippyDame]

Poor you, not surprised you feel unwell with such a low FT4

The total T4 test measures the T4 that is both attached to proteins and floating free in the blood.

The free T4 test measures only the T4 that is floating free in the blood.

The same applies to TT3 and FT3

FT3 and FT4 can interact with the body’s tissues, so they are considered a better indicator of thyroid function than Total results.

We recommend use of the Free labs.

TSH fluctuates throughout the day so, alone, is not a reliable test....

We need both Frees to sit roughly approaching 75% through the ref range

We advise the following be tested

TSH, FT4, FT3, vit D, vit B12, folate and ferritin...and if not previously tested the antobodies TPO and Tg, for Thyroid Autoimmune / Hashimoto's.

If you wish comment on labs post the results including reference....we're all here to help. Just ask!

[woofa27 in reply to DippyDame]

So, I've never been clear about whether that bound t4 and indeed, any bound t3, can be detached from that protein by the body and become free t4 and free t3 if we need it at a later date, or whether once thyroid hormone is bound, is it completely redundant? Does anyone know the answer to this?

[helvella Administrator in reply to woofa27]

Yes - T4 can and does get unbound. In that sense, the TT4 acts as a reservoir to top up FT4. It also provides a means for T4 to be transported round the body while being safely bound and not able to have any effect on the body as it flows round.

While TT4 can rise and fall significantly, the body maintains the free T4 level within quite tight limits.

(Similarly for T3.)

Only something like 1% of our T4 is free - 99% is bound.

Only something like 0.3% of our T3 is free - 99.7% is bound.

[Jo5454 in reply to DippyDame]

Thank you!Thats great…I’ve double checked my most recent test I had on day I started loading dose.Had no choice of time due to having to take any apptmt, but was 9.30, & hadnt fasted. Due to feeling so unwell with pretty nasty neuro symptoms was just concentrating on b12 side of things.Just double checked, over exaggerated FT4 it seems, it was actually 12.2 (9-19.1) thought it was bit lower than that! On pinpricks TSH has been between 2-just over 3 last year, was 1,53 (0.35-4.94)

My ferritin has lowered from 48 to 37 since loading dose, taking ferrous fumerate but awaiting Three Arrows heme to arrive.

Last vit d in 60’s, so will now recheck, take a daily supplement.

Folate 7.6 (3.1-20.5) take a folic acid supplement most of time.

B12 was 608 when severe neuro symptoms & had come to halt feeling very ill. Had been trialling sublinguals through covid, but been allowed bk on injections, every 2 monthly instead of monthly before, so work in progress at mo as have a Functional defic, levels 1800 after loading dose.

Cholesterol gone up from 3.9 to 5.3, but no changes in diet, eat v. healthily- also developed milk into,seance & borderline gluten so am dairy/gluten free.

MCH overrange, lymphocytes under, h bA12 fine, potassium bottom range.

Thought I’d recheck thyroid with home test, fasting & earlier to see if it’s improved since back on b12 jabs & include vit d & other bits too…I’ve assumed all the symptoms linking to b12/iron probs, but not so sure!

Thanks so much…

[helvella Administrator]

The difference between Total T4 and Free T4 is, of course, the T4 that is bound to blood proteins.

The big problem in using TT4 is that the amounts of binding proteins can and do rise and fall - even while FT4 could remain more or less stable.

For one example, estrogen affects binding proteins. Hence, TT4 varies with menstrual cycle.

And some people have little binding protein (a fairly rare genetic trait).

So TT4 usually tells us little of interest.

Ferritin that low really does need action.

[woofa27 in reply to helvella]

How do you know all this stuff - you're so knowledgeable!!! I hear what you're saying about tt4 being highly varyiable, but surely, if you had one individual who has tt4 top of the range and another with tt4 bottom of the range, but the same free t4 levels, then the first individual is a darned sight better off than the second. Surely it is still of interest?

[helvella Administrator in reply to woofa27]

But those results could be in the same individual! Just different points in menstrual cycle, etc.

Why does having a higher TT4 make someone better off than someone having a low TT4?

People with virtually no TT4 - due to having no (or very low) thyroid binding globulin - might live their entire lives in total ignorance and never have any health issues obviously connected to thyroid hormone levels.

The high TT4 does mean they have a larger reservoir, a bigger buffer, but most of the time that seems to have little real impact.

One of the reasons FT4 has come to prominence, and TT4 has faded, is that TT4 is so susceptible to incorrect interpretation.

[woofa27 in reply to helvella]

Darn it, I knew you'd say something along those lines! But surely ft4 levels are just as susceptible to incorrect interpretation too. If I've just spent the day sitting on my somewhat ample arse, prior to blood test, won't my ft4 levels be higher than if I've spent the whole of the previous day weight lifting, unless I have adequate bound t4 levels to compensate for that, which, quite frankly, the current dosing system does not seem to allow me to have. I suppose I'm just thinking that for all of us lucky people relying on exogenous hormones, that maybe with a higher dose of levothyroxine we could potentially give us higher reserves of t4 for, for example, for all those marathons we all so frequently find the energy to run!!! I know this is the reason we're all here on this platform, but the entire system of moderating levels and medicating patients to a satisfactory level just seems so so flawed and surely making sure our tt4 levels and tt3 levels are also at a reasonable percentage through the ranges would give us a better fighting chance.

In what way did tt4 prove to be susceptible to misinterpretation, was this simply when tested in isolation from the free t4 levels? Or was there something more complex going on?

And also, thank you for your, as always, detailed and knowledgeable replies 😘

[Jo5454 in reply to helvella]

Thanks Helvella…didn’t realise that!

Yes, I’m working on iron stores, not that Dr noticed it! you sent me that wonderful iron info sheet! Wondered why my Three Arrows hadn’t arrived, apparently it was on pre-order, doh, but should soon be on way!