Thyroid UK
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T4 and T3 conversion ratios & Antibody ranges

Hi there,

I have recently been diagnosed with Hypo (previously classed as subclinical) and after talking I have persuaded my DR to test both my T3 and T4 levels -

My results are -

T3- 3.8 (unfortunately only FT3 done and not Active T3 as well)

T4 - 9.2

TSH - 17.01

Antithyroid Peroxidase 33

She states that my Antibody levels are nothing to worry about!

She also doesn't seem worried that my conversion ratio seems to work out at 2.4 (t4/t3) I have heard that the conversion ratio to active T3 should be 4 or more, is this right and and would I be correct in thinking that my active T3 levels would be lower than my full T3 levels, therefore my conversion is probably even lower?

What is usually the cause of lowered conversion please?

Currently I have not started taking my Thyroxine as I don't feel massively unwell and I am going to try and bring my levels back right with dietary changes and acupuncture.

Please could you offer any knowledge you have on it all concerning the conversions and also the antibody ranges ???

Thank you

12 Replies


Thyroid peroxidase antibodies 33 are usually just under 34 which is considered positive in some areas. You can't conclusively rule out autoimmune thyroiditis (Hashimoto's) with that result, and some people are negative for thyroid peroxidase but positive for thyroglobulin antibodies which NHS doesn't test.

Your conversion rates will be off until you are optimally medicated and thyroid levels are euthyroid (normal). TSH is 17 because the pituitary has detected low T4 and T3 hormones. Your FT4 and FT3 are only as good as they are because the TSH is flogging the thyroid to produce hormone.

There is no active FT3. There is total T3 (TT3) which is T3 bound to proteins and free T3 (FT3) T3 unbound to proteins. TT3 isn't used much in the UK, FT3 is the preferred test.

TSH >10 is considered to be overtly hypothyroid. You are very fortunate not to be symptomatic but should reconsider starting Levothyroxine to prevent adverse health outcomes and symptoms which will occur without treatment. You cannot replace low thyroid hormone with dietary changes and acupuncture.

For maximum absorption Levothyroxine should be taken with water 1 hour before, or 2 hours after, food and drink, 2 hours away from other medication and supplements, and 4 hours away from calcium, iron, vitamin D supplements and oestrogen.

It takes 7-10 days for Levothyroxine to be absorbed before it starts working and it will take up to six weeks to feel the full impact of the dose. Symptoms may lag behind good biochemistry by several months.

You should have a follow up thyroid test 6-8 weeks after starting Levothyroxine. Arrange an early morning and fasting (water only) blood draw when TSH is highest, and take Levothyroxine after your blood draw.


Sandrafrog It would really help if you put ranges with your results. And I presume T4 = FT4 and T3 = FT3.

I'm not sure what you mean by the 'active T3 test'. The usual test is Free T3, sometimes Total T3 is tested which isn't as useful as the Free T3.

To get your conversion ratio, it's FT4 divided by FT3. The ratio should be 4:1 or less, not more. So your conversion is showing as very good with those results.

T4 - the inactive hormone gets converted to T3 - the active hormone.

What is the range for TPO antibodies? Usually we see <34. If that is the range for yours, then you are so close to the top that even though they aren't showing positive at the moment, repeat testing at some point may do so, which would then confirm autoimmune thyroid disease. TG antibodies should really also be tested, as people can have negative TPO but positive TG antibodies.

Guessing the ranges from what we usually see, your TSH is a long way over range, your FT4 is either very low or under range, and I'd say FT3 is very low. All confirms hypothyroidism. Your thyroid gland is failing and you should start taking your Levo, I don't think dietary changes and acupuncture will make your thyroid work properly again. If you have autoimmune thyroid disease, the antibodies gradually destroy it so there's no way you can stop that.

Dietary changes in the way of adopting a gluten free diet can help reduce antibodies, so that's a good idea.

Supplementing with selenium can also help reduce antibodies, and it helps with conversion of T4 to T3 to, so taking L-selenomethionine 200mcg daily is a good idea.


What do you mean by the 'active' T3? FT3 is the active one.

It's difficult to tell without the ranges, but it doesn't look to me as if you have a conversion problem. And your TPOab doeszn't look high, either. The ranges are set by the labs, so you really need to get hold of the ranges used by the lab that did the tests. Just any old range won't do.

Ratios are for healthy people. They really don't mean much when you're hypo. But, if I were you, I'd start that levo ASAP, and nip it in the bud, before you do start to feel ill! :)


Thank you all for your responses, I have just called my surgery and got the ranges -

So my results are as follows

T3 - 3.8 (3.9-6.8)

T4 - 9.2 (11.0 - 23.0)

TSH - 17.01 (0.35 - 5.00)

My theory with the dietary changes and acupuncture is to reverse the autoimmune response that is potentially causing my condition. I am being tested again in 6 weeks, so if I have had no improvement from the holistic approach, I will begin the Levo at that point.

As you have all pointed out my errors in the comments, I still have learning to do on this subject, but I am sure with your help I will start to understand it all a lot more.

Thanks again to you all

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Just keep in mind that tsh and other hormones fluctuate all day every day so your tsh may well go down whether or not you're on a restrictive diet or having acupuncture. I went down that route (tcm) and my tsh did go down but I became increasingly unwell and when I was finally 'ready' to go on levo I had a struggle getting my doctor to prescribe it as I was then within range.

Of course you have to do whatever you feel is the right thing and I'm not trying to take the wind out of your sails, just ensure you keep to your schedule and don't allow yourself to decline indefinitely. It can be hard to tear yourself from a path that you want to go in a certain direction. I became very ill despite my tsh 'responding' to acupuncture/tcm.


Hi Puncturedbicycle, thank you for your advice, how long did you try acupuncture for? Why were your levels like before you tried it?

What I am confused about- when my levels were classed as subclinical, I felt much worse than I do now, I was falling asleep on a washing line, I had very little energy. But I'm feeling a lot better of late, so I was very shocked that my levels are now clinical!

Did you make any or need to try making any dietary changes along with your acupuncture?

I hope you have managed to get yourself back to health now.

Thanks again for reply.


No worries. I don't know offhand how long it was - it was about 7 years ago - but I think 6-10 months of herbs and acupuncture and some qigong (although truth be told I hated qigong and it made me feel ill so I didn't do it very much). There was also a month's' wait to see the doctor, which I can't believe I went along w now I think about it.

I also saw a doctor in Bath who is a gp as well as a Chinese meds doctor and he advised a diet of root veg (I think that is a seasonal Chinese thing though, I don't know how specific it is to uat), lean protein, warm foods and little fat. I'm sure there were other things! That was a one-off though and most of the time I saw someone in Hammersmith who gave me herbs as well as acupuncture. My tsh went from 30ish to around 5.

Like you I didn't necessarily feel worst w the highest tsh, I think I'd been on that trajectory for a while, feeling increasingly tired, craving carbs, and felt pretty bad when diagnosed, but after such a long time w no real relief I felt really bad when my tsh was 5. That's when I had trouble getting my script back.

Eventually I had about six good months after adding some t3 to my levo, but I crashed and have never really got back to feeling well again.

May I ask have you had any 'incident' that first made you suspect something was wrong? I was running at the gym (gentle pace, only increasing my sessions by a single minute so not really serous training) and I got off the treadmill and felt like all my bones turned to jelly. I felt like I might have to get a taxi home as I wasn't sure I could drive. I thought maybe I had some post-viral thing or whatever so I took some time off but I didn't really recover and not long after that I was diagnosed.


Well you definitely gave it a fair run, sounds like you spent a fortune on trying it all. I've already started qigong about 1 months ago, I'm loving it, but we would do to all be the same, plus there are different types of qigong.

No 'accident' whilst not on levo, I was tested as a routine check up really, I was worried about staying hormone contraception due to the long history of heart disease in my family and it was noticed my thyroid was slightly under, that was 4 years ago. When I first tried Levo (25mg) about 1 yr ago as I was feeling very tired then, I felt more tired and I fell twice whilst out on my morning walk, I literally fell over my own foot, like it didnt lift up correctly. That all stopped when I stopped taking the levo as it gave me incredibly bad heart burn and I felt worse! But a couple of acupuncture sessions after that and I felt ok again. I'm currently avoiding bread and in a few weeks after my dissertation is due in I will give up everything else, but I need to keep my focus on my dissertation for the very short term.


To be fair, 25 is such a tiny dose it may make you feel worse and there is not often a good reason to start anyone on less than 50. Often people post their results here and after a starting dose of 25 the tsh may rise and t3/t4 fall. But I am no great advocate for levo, and it doesn't suit everyone.

In any case I wish you all the best w your efforts and good luck w your dissertation!

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Thank you 😊


If you are keen to try the holistic approach first, then going gluten free or even autoimmune paleo may help. Also look at leaky gut, low stomach acid and possible gut infections


Thank you SlowDragon, I will most certainly check these out.



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