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Thyroid UK
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How much T3: T4 in blood ?

This is all new to me and there is so much information to take on board.

I'm starting on the road to self medicating and have dropped 25 mcg of levo to substitute for a quarter tab of 25 mcg cynomel. My conversion has been hampered by digestive issues and D3 and B12 deficiencies.

I was interested in reading on here that there are different views about what optimum blood results should look like (given the obvious fact everyone is different). I had read somewhere that T4 should be in the lower 50% of the range and T3 in the upper 25-30 % of the range. I have also seen suggestions that ideal blood results should show a 1: 4 ratio of T3 : T4 which would reflect another view I've seen that suggests both T3 And T4 should be in the upper part of the range.

Does it depend on how efficient a person's conversion is?

Im hoping that by the time I get a blood test in about 4 weeks I will have less T4 (was over range) and more T3 (was in lower 25%). However I have been addressing the deficiencies of D3 and B12 for a week while taking only the reduced dose of Levo (125). This morning I took an additional quarter cynomel as my blood temperature had dropped to 36.

If i get a result in a few weeks that show D3 and B12 both good, do I stop the supplements or assume I will always need them (I've been Hashi for about 8 years) ? How do I know the T3 is going up as a result of better conversion or the small dose of T3, or does it not matter ? And what am I looking for as a good result to know whether or not to make any adjustments?

Any thoughts gratefully received.

16 Replies


Optimum blood level is the level at which your symptoms are relieved. For some people that will mean FT3 halfway through range, for others somewhere in the top third of range, and for a few people at the very top of range.

It depends how far over range your FT4 was as to how quickly it will drop into range. If it was mildly over range a 25mcg reduction should see it within range within 4 weeks. The 6.25mcg T3 will raise FT3 and will also improve T4 to T3 conversion which will 'use up' some of the high FT4.

The point of checking temperature when taking T3 is to note any spikes in temperature which may indicate over medication. Some people have naturally low temperature and if they continually up their dose to raise their temperature they will become over medicated.

Once your B12 and vitamin D levels are optimal you may need to take a lower dose to maintain levels.


Wantie I'm not sure where you got the information that FT4 should be in lower 50% of it's range. The aim of a hypo patient is generally for TSH to be 1 or below or wherever it is needed for FT4 and FT3 to be in the upper part of their respective reference ranges if that is where you feel well. It's generally said for FT4 to be in the upper third and FT3 in the upper quarter. That's when treated with Levo only. Add T3 into the mix and it has the effect, generally, of lowering FT4 and TSH. So when T3 is added it FT3 that matters and TSH and FT4 aren't so relevant.

As far as conversion is concerned, yes member Diogenes (who is an advisor to ThyroidUK) states that the FT4: FT3 ratio should be 4:1 or below. That shows how well you're converting when on Levo when treated. Add T3 into the mix and you can't use that ratio, purely because it's now measuring FT3 which has been helped by the addition of T3 so you can't measure how FT4 is converting because of the boost FT3 is getting from the T3.

So all that matters, when taking T3 in any form, is that your FT3 is within range. You need to keep your eye on that result and adjust dose if necessary. And if you want to see how much is getting into your cells then you need to do a thyroid urine test with Genova.

My FT4 was very over range with FT3 just about half way. I did exactly what you are doing, it took a few reductions (over a few months) of Levo with a few gradual increases of T3 to bring my FT4 down to something like 18 (12-22) and FT3 up to 6+ (3.1-6.8).

As far as your vitamin levels are concerned, once they've reached the recommended level then you need to continue supplementing at a maintenance dose. It's advisable to re-test Vit D once or twice a year and adjust dose as necessary. B12 result will just refelect the fact that you are Supplementing, so if you reach over 1000 it's best to reduce dose but maintain the level around 900-1000 which is the level recommended by the Pernicious Anaemia Society.

As you have Hashi's, are you gluten free and supplementing with selenium to help reduce antibodies?


I can only agree with what Seaside Susie says! When on a combination of T3 and T4 (be it NDT or synthetic drugs), your hormone levels will look different compared to when you take T4 drugs only.

When my FT4 levels are midrange or slightly above, on NDT, my FT3 levels skyrocket. Through trial and error, I have found that I get the best results (complete resolution of hypo symptoms without any hyper symptoms) on a dose of NDT which results in FT4 levels at bottom of range (0.9; ref 0.8-1.5) and FT3 levels of 2.9 (ref 1.7-3.7) 24 h after taking NDT. This means that my FT3 levels were +/- 20% higher on the previous day, so somewhere around 3.4. This is where I feel best.

I am not saying this works for everyone, but Seaside Susie is right about the effects of added T3; it tends to lower or even suppress your TSH and also lower your FT4 levels. I am getting more T4 now through NDT than I was taking when on levothyroxine alone; yet, my FT4 levels are much lower now than on T4 only. This proves to me that the addition of T3 lowers FT4 levels.

Most recommendations you find online (FT4 levels close to or at upper normal limit, FT3 levels midrange or slightly above, TSH between 1-2, etc) apply to patients taking T4 only drugs. I am not sure how valid they are once you add T3 to the mix; in my own experience, not so much.


Hi Anna69 that's really interesting. To discover the relative levels of each that make you feel best, how often do you take blood tests and over what sort of timescales do you adjust? I'm keeping a record of all my supplements, and the levo and cynomel doses as well as symptoms but I'm assuming to stick with this regime for 5 weeks before I get a blood done or change anything. I don't feel confident to keep incrementally increasing the T3 until I feel good as I have only just gone gluten free, have only just started to sort out B12 zinc and vit D deficiencies and until I have reaped the benefits of these changes I can't really be sure what's going on. Plus my conversion rate may improve, who knows? I am trying to do this with a view of a slow and permanent improvement so staying patient is important I guess.


Nowadays, I only take blood tests once a year, right before seeing my hormone doctor which I usually do in August. I decrease and increase my dosage based on symptoms more than anything. It may not be ideal, but I have learned to interpret my symptoms pretty well and usually recognise the first signs of being either hypo- or hyperthyroid pretty fast.


Yes that's what I'd like to be able to do. I'm on a bit of a learning curve just now. But it's better than feeling abandoned and completely shunned. Thanks


Well, it took me well over a decade to learn how to distinguish hypo from hyper symptoms...so hang in there, you'll get it:-)


That's really helpful Seaside Susie. I started all this when my gut became disfunctional and all doctor wanted to do was prescribe probiotics and reduce my levo. I started going gluten free as I started to reduce my levo..everso slightly, about two weeks ago. Apart from a couple of mistakes like thinking rye bread was gluten free, it's made a huge difference. Thankfully I appear to be ok with dairy...which is my passion.

I am still a bit confused about blood results. It showed obvious B12 deficiency 189 ((197-771) pg/ mL. And D 15.8 (deficient was deemed under 20) pg/ mL by the lab. But my lymphocytes are also low 1470 (1500 - 4000). / mm3. And my coefficient of saturation iron is high at 55 %, serum iron is 34.4 (5.83 - 34.5) umol/ L and transferrin 2.51 (2.00-3.60) g/L. Magnesium ok 0.9 (0.66-1.07) mmol/L. There also seems to be a small decrease in renal function determined by the rate of blood filtration using something called CKD-ÉPI (sorry I'm in France, most of its pretty obvious and they use same techniques and methods) mines 66 mL/min but labs say better if over 90.

I have a blood test in about 4-5 weeks so hoping I can do good diet and sensible self medicating (very incremental) to make a difference. I had intended to stay off all supplements a week before blood test to see where my natural levels had got to.

Any thoughts most welcome.


Wantie For Vit D, I don't know the recommended level in pg/ml. I don't know how that compares to nmol/L which we use here in the UK or ng/ml which seems to be used in the US. If you can find out how to convert your 15.8pg/ml then you need to aim for the Vit D Council's recommended levels of

100-150nmol/L or


B12 needs to be at the very top of it's range, even 900-1000 as mentioned.

Was folate tested? This works with B12. If folate was very low then you should take your B12 and folate results over to the Pernicious Anaemia Society forum here on Health Unlocked for further advice


Other tests you'll need to check here, as I don't have the knowledge to offer any suggestions


If you speak French, there is Labtestsonline France which might be better for you.

This might help with your iron results

rt3-adrenals.org/Iron_test_... and

Go to the second link down - Iron Overload with Anaemia Reference Chart here (I can't link to PDFs on my tablet)



Many thanks for all the additional information. I'm going to keep doing what I'm doing just now and review after the blood test in a few weeks. I have no sympathetic doctor or endo here. Do you know how I can find a well informed thyroid consultant in Scotland ? I think even a private consultation from time to time would be useful.


Wantie If you email louise.roberts@thyroiduk.org.uk she will send you the list of thyroid friendly endos. Also, you can ask for recommendations on the forum but replies have to be by private message.

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Once again thanks. It's easy to get really down with all this, but I've found this forum a great help just connecting with others. I'm going to email Louise just now.


Hi SeasideSuzy. I'm really nervous about my next appointment with my GP as he has commented on my latest blood results and wants 'to discuss". I'm prescribed 3.75 mls of liquid thyroxine (80mcgs) and 10mcgs of T3. I also supplement with T3 as I feel under medicated on the above prescription. I haven't told my GP that I order from overseas. My results show my THS is almost suppressed and my F T4 is 9.8 (12 - 22.0). My FT3 is 4.3 (3.1 - 6.8). Most of the time I feel ok but it can be variable. At no time do I feel over medicated, but I'm sure I will have to defend my corner and explain why I have these results. I only have a few minutes to explain myself, so I'm anticipating him getting impatient and dismissing anything I say. Any comments on my results or a way ahead of convincing him that my results are acceptable would be very much appreciated.



SeasideSusie may not see your question tagged on to the end of Wantie's post. Please write your own post.

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"THS is almost suppressed

F T4 is 9.8 (12 - 22.0)

FT3 is 4.3 (3.1 - 6.8)"

There is nothing amiss with those results. Your TSH is not suppressed, I'm guessing as it's low it might be under range but your FT3 is well within range and that is the one that matters. As you are taking T3 your FT4 isn't that much of a surprise. When taking T3 both TSH and FT4 will lower, and a suppressed TSH isn't uncommon. Considering where your FT3 is within it's range, there is room for an increase if your symptomatic.

"Most of the time I feel ok but it can be variable. At no time do I feel over medicated"

Have you had thyroid antibodies tested - TPO and TG? Also, have you had the following tested? If so, post the results with reference ranges for comment. If not it's a good idea to get them tested as we Hypos need optimal (not just in range) levels for thyroid hormone to work properly:

Vit D





Hi, yes it's not easy. I think in the long term I will need to get it prescribed. However since I'm only using a quarter tablet each day, one box should last 4 months. By then I will know if it's the right thing for me. I had to try several pharmacies and they all did look at me a bit suspiciously. I suspect there is probably a bit of a black market in it for keeping ultra slim ! I wouldn't be able to source it locally as I live in a small town. I got it when I was in Paris feeling desperate !


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