Thyroid UK
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Thyroid Hormone Blood Tests - Whats the Point????

Since Feb 12 I have been paying for private blood tests (GP/Labs hopeless).

I have never on a blood test looked like I have severe HyPO, HyPO yes but not severe.

Because of a post and passing comment on here I decided to have a blood test & a urine test for thyroid hormones within 48hrs of each other.

The serum blood test showed a good result for TSH, T4 & T3.

HOWEVER, the urine test showed a VERY Low result for T4 & T3.

Serum blood is a snapshot in time. Urine is a 24hr picture. I believe Dr P does not favour serum blood tests. I now can see why, they give a very false picture.

I feel frustrated to have wasted money on serum tests when it has given a fake poicture of whether the hormone is actually gettig into the cells. More importantly I was oblivious to the fact that my T4/T3 was actually not doing anything in my cells.

That the NDT I take is simply floating around in my blood.




It is my understanding that if the hormone is not getting into our cells then we will remain HyPO?

What is a puzzle to me is that my symptoms or lack of them does not reflect the low T4/T3 urine test.

I take a weeny dose of NDT, perhaps I am just fortunate.

I am now on a mission to see how I can improve the status quo of my urine test results.

My ferritin, iron, saturation B12, D3 are all not too bad as I have worked on them all last year and still now I supplement.

I suspect that the mercury in my body from amalgams (all now removed) is blocking the uptake of T3 in my cells. Selenium is required to convert T4 to T3, my Selenium is deficient, despite supplementing it. Genova suggest that Selenium can be impaired by the presence of heavy metals such as mercury, cadmium and lead.

I wonder if there are a LOT more HyPO people who have this underlying issue too.

My gut instinct is that it could well be a big clue to some folks thyroid ailments. But that's just my take on it.


14 Replies

Am wondering a couple of things.

What time of day did you have the blood draw?

Have you got any references specifically to mercury blocking uptake of T3 in your cells? I am trying to understand which part of the T3 getting taken up is blocked by mercury. The transport through the cell wall? The TRalpha or TRbeta receptors?

Also, would you share the test results (and,of course, reference ranges) so that we can see what you mean about the differences between blood and urine?



Hi Helvella

Blood draw was at 09.30am - I had not taken NDT for 26hrs.

Reference material re mercury and cells - no. DDI Lab in USA and Genova Lab UK both have the same comments about Selenium deficiency, cellular uptake of T3 and Mercury + other metals.

Test results and ranges

SEROM 11/1/13

TSH0.65mIU/L0.27 - 4.2

T416.2pmol/L12 - 22.00

Free T34.4pmol/L3.1 - 6.8

URINE 13/1/13

T4193 LOWpmol/L347 - 1994

T3354 LOW pmol/L592 - 1850

A question for you







hi JLT,

I can't answer for the whole forum but I can give 'my opinion'/version:

I do not believe in blood tests anymore at all, as dear Dr Lowe used to say: they are only useful when they are 'very very out of range' (nothing I have seen published on this forum 'yet').

I don't know enough about the accuracy (or not) of urine results but one thing for sure: if urine was a reliable test to show if your cells are uptaking/using the thyroid hormone or not then all the 'good/alternative' doctors we know of would be using them and pushing for these to be used, however this is not the case.


It is frequently mentioned that blood tests have problems. For example, that TSH does not always respond as the "standard theory" suggests it should, that they are dependent on time of day, medicines taken, etc.

But whilst people have put forward that urine tests are better, there is little good evidence that I have seen.

And I note that Genova say:

It is important to use this test as an adjunct to other indicators of thyroid function, such as body temperature, symptomology and standard blood thyroid tests.

Which rather suggests they are not suggesting urine tests as a replacement for blood tests.




Dr P asked me to do the Thyroid Urine test and I believe he trusts the urine more than the blood. My T3 in blood was high, however the urine showed it was actually low, so Dr P said it is high in the blood but it's not going into your cells. Conversion issue.


I don't understand it though.....

urine is the product of kidneys, kidneys filter BLOOD, how on earth is the urine telling you that your cells are not 'getting it'???

to me it suggests the opposite....that you are using it as you are excreting less of it? :D

sorry am just trying to understand that is all :) x

1 like

ha ha :-))


ok ok, I have been thinking about this one:

they say that to ascertain if you have iodine deficiency you should take iodine (can't remember the amount) and then straight after that do a 24hr urine collection, the more deficient one is in iodine the LESS is excreted in urine.

therefore....if for T3 and T4 this is the same it would suggest that yes you are hypo if you have low results, however it does NOT mean that your cells are not using it is not a test to prove you have thyroid hormone resistance or a conversion problem........


And it might be that you would actually be testing something else entirely to prove that thyroid hormone is being utilised by cells. I quote from a recent paper:

Alternative biomarkers to assess the supply of the organism with thyroid hormones include resting heart rate and other determinants of cardiac output, oxygen consumption, respiratory quotient, thermogenesis, methylhistidine excretion and plasma levels of lipids, SHBG, sclerostin, ceruloplasmin, lead, copper, arsenic, or MBL. These parameters have not been well evaluated, however, and due to the fact that they are subject to multiple extrathyroidal influencing factors they are not expected to deliver superior results as diagnostic tools.



The reason it quite simply that we try and encourage people to stick with their NHS GP if they can - it is cheaper for a start - and the vast majority of NHS GPs would not accept the results of a thyroid urine test.

We try to offer a wide range of suggestions for diagnosis and treatment - this is why we have information about the urine testing on our website. We are also currently conducting a research study comparing the blood tests to the urine tests.

Hope this helps.


Thyroid UK


I think this thread shows that we are not really sure how to interpret the urine thyroid test.

I expect that's the reason it's not used on the NHS.

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Hi, I know this post is 2 years old but I have just had a urine test like you did, which shows very low T3 ( I have been on NDT) for nearly 2 years now but not doing well).

I cannot understand how the test can show what your body is doing, or not doing with the T3. Urine is a bi-product of the kidneys so isn't the T3 reading showing that excess is being excreted? How does it show how the body is using the T3? Not much info on this test out there.

Very confused about changing to adding T3 to my NDT dose ( doc says it's a conversion problem but how does that urine test confirm that? ) as my bloods show relatively normal results compared to the urine test although I know I am not feeling well on just NDT.

Actually, it did show the T4 to be in the lower end or normal, which does correspond to the blood test level ( 14.1). However the T3 was very low ( 300's) but blood test is fine at 5.6 ( mid-range ). So, not sure what that actually means, and it seems others are very dubious as well.

I am rather nervous of adding T3. I do feel better but with unpleasant jittery-ness and headaches and brain fog, if I go above a certain level on the NDT. EIther that or I maybe I am reacting to something in the tablets ( Erfa is supposed to be a good one). Constant Internal trembling on only 1 1/4 grains.

I would appreciated any more info that you may have to offer about the urine test. It all helps to build the picture because the private docs I've seen so far and my GP sure don't seem know much about treating Hashis, or NDT, or T3! They all have different ideas and are mucking me about each time I try someone different in the hope that they will the "the one" to help sort this out. 25years is a long time to be struggling alone with this blasted thyroid illness.Thanks - and hoping you are getting on well with yours.


I've never done a urine test for thyroid hormones because I wouldn't understand the results, and I can't work out to my own satisfaction what results would be good.

My logic was :

Imagine a person who is completely healthy. They don't have any autoimmune problems, their thyroid is a thing of beauty, they are fit and well in every way.

Having imagined that lucky person, what results would I expect from them with a thyroid hormone urine test?

1) Lots of thyroid hormone (T4 and T3) being excreted because the body is taking what it needs and getting rid of the rest?

2) Very little thyroid hormone being excreted because the body is being efficient and only making/using what is necessary?

3) Some other combination of high/low T4/T3 for which I could probably come up with a possible scenario to explain it.

Then I thought... If I can't work out (and understand the reasons behind) the results for a healthy person, what chance do I have for myself? So I've stuck with the status quo and gone for blood tests. It makes life easier.

I've had the same arguments with myself about urine tests for iodine. Suppose I had a high reading for iodine in my urine. Does that mean...

1) I am taking in too much iodine, and my body is excreting the iodine I don't need. Therefore I should cut down on iodine containing foods in my diet.

2) I am taking in a sensible amount of iodine but my body is already replete, so I am losing the iodine I take in.

3) I am taking in the right amount of iodine, but my body (for some unknown reason) is unable to metabolise that iodine and use it where it is needed, so I just excrete it anyway. Nevertheless my body is still crying out for iodine and isn't getting it.

So... I avoid urine tests. I don't understand them!


Thanks for that. I'm speaking to Dr P tomorrow so will get him to explain the discrepancy. In the meantime his protocol has made me feel even worse so not convinced!


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