RT3 in urine too low, meaning?

Hi guys,

the thyroid is my study object for a while now and I have a result which I still can't explain and understand.

I have had a couple of blood tests in the past 7 years for the thyroid and they always were not good. Am finally getting treatment since november 2014.

In november 2013 I joined a scientific research which was done in a hospital (so no alternative testing but in a hospital lab). They tested a lot via blood and some things via urine. Via urine they tested the thyroid function (still surprises me as I thought this was not considered reliable in the regular medicine). This were my results of the 24h urine test:

T4: 1026 pmol/24u (range 1800 - 3000)

T3: 329 pmol/24u (range 800 - 1800)

Reverse T3: 30 pmol/24u (range 46 - 130)

Now here what I don't understand..The rt3 result. I only find that you need to get it tested because of when it's too high. Mine was (is?) too low, what does that mean?

I hope anybody can tell me.

Last edited by

17 Replies

  • As an educated amateur, I'd say that everything was low and your fT3 wasn't low because rT3 was high, so nothing other than hypothyroid going on. Didn't they explain anything to you at the hospital? Or did you not think to ask at the time because you felt so awful?

    But yes, you are correct. According to research papers in Pubmed the measurement of urinary output of thyroid hormones was deemed to not be reliable and that's why bood is tested instead. So I'm also wondering why they bothered to do this. Where was this done? As in country. Some places right now, like India, Turkey, and Spain are doing some primary research which is actually of value. Basic research has become affordable while at the same time other countries have gone super our of orbit high tech, molecular and whatnot.

  • Because it was for a scientific research I didn't see a doctor or somebody to explain this. I had to fill in some paperwork and then a nurse took the blood and I had to do the urine test. Normally you don't get any personal results so that I got these is not normal and probably the reason I didn't saw a doctor. I only have books/internet and my GP to find explanation.

    I'm from Europe, the only urine testing for thyroid I can find in my country are from alternative labs. But they did test this in a hospital so that is saying something..Although my GP wanted a blood test after this and she didn't took notice of the urine results.

  • Flower, T4 converts to something like 80% T3 and 20% rT3 so I'm guessing that as your T4 and T3 were low it follows that rT3 would also be low.

  • Thank you! Sometimes the explanation is easy..Too easy so then I'm wondering if it's the right explanation.

  • I hope you are starting to feel better now that you are being treated.

  • why aren't the frees done in Urine testing? These are Totals..then not very useful. A low t4 would give you a low rt3 reading.

  • What would "free" mean in urine testing?

    The Free/Total distinction for blood tests is "How much of the hormone is bound to proteins?"

    Urine, though it may contain some protein, doesn't have a carefully controlled level of thyroid binding globulin, transthyretin and albumin.

  • Just pondering the urine side of things. I've no idea in the past as to why it was deemed unreliable so again guessing but could it be checking again alongside a blood result because a possible flaw been suspected in the earlier testing or that better instrumentation could give an acceptable result? One aspect of research could be to test different/better ways of doing things and not always searching for new discoveries as such. Getting blood out of me is a real problem these days and I'm sure I'm not the only one. It can be traumatic for some and it could be cheaper or allow us to self test, or may be its trying to eliminate any chance of cross infection.

  • It would be very interesting to know if low rT3 has any effect at all. Ranges are sometimes simply on the basis of observation with few or no clinical correlates.

    However, low T3and rT3 would probably suggest low T2 (as T2 comes from conversion of both T3 and rT3). I wonder what effects that might have?

  • Exactly, can't find anything about low rt3. But my guess is that as the T4 and T3 rise, rt3 does too so it all becomes normal.

  • The doctor I see (functional medicine specialist) always has a blood test as well as a urine test done to measure thyroid hormones. He says that the urine test is a more reliable measure of the cell level absorption of thyroid hormones. I would be very interested to receive any links to research that shows urine tests being unreliable.

  • Dr D in Paris consideres urine tests to be Superior to blood. He says that the blood test gives you a photo, but the urine test gives you a film. Not quite sure what he meant by that...

  • Hi, my understanding of photo and film is that a blood test will only reflect what is happening at that point in time (snapshot) but the film aspect for urine (usually over 24hrs.) gives a wider picture and therefore more accurate as to what is in your body. No expert but this is how is was explained to me. Hope it helps.

  • I guess because the urine is over a period of 24 hours?

  • Yes, of course! Silly me! lol I've even done it, but completely forgot! That's brain fog for you!

  • Remember this from helvella recently:


    It seems to me that peeing in a pot for 24hrs or taking blood for some point in the day is of little diagnostic use.

    Why does TSH and T3 rise together at night, T4 is just there like a storage pot, in group of 'normal' people. Does anyone understand the mechanism of this process, it must be critical? Critical for those who have a poor functioning thyroid system.

    The best time for checking, when the very active thyroid system is at it's most active, is midnight. Taking blood at 0900hrs for 1100hrs collection to the lab seems to tell one little information. Ratios would be of little help as T4, T3 and TSH seem to produce little change. Midnight ratios may show up the failures in a failing thyroid system.

  • I agree, and even that most docs don't know (that TSH is highest midnight).

    I don't know if it's true but I've read that TSH and the hormones itself rise midnight because this way a person woke up with energy. So the body is already starting up while sleeping so you can be active when you wake up.

    Also read that 30% of hypothyroid people are missed cause of taking blood midday and not in the early morning. So if you ask me they should say that if you get a thyroid blood test this must be done in the early morning.

You may also like...