Thyroid UK
89,212 members103,718 posts

Am I able to convert ft4 to ft3?

My Feb 2017 thyroid results were "normal" even though I was having symptoms even then.

Tsh 1.8

Ft4 1.16

Ft3 3.1

Results in May 2017

Tsh 1.9

Ft4 .8

Ft3 2.0

I was told in May I was normal by Endo even though I felt like complete crap.

Two weeks later I went to another doctor who tested me again.

Tsh 2.1

Ft4 1.0

Ft3 2.6

Tsh and free t4 and free t3 went all went up in those two weeks.

My question is, does it look like I do ok converting ft4 to ft3? So if I add a t4 medication, this should help hypo symptoms (since I can convert), not make them worse?

14 Replies

Sorry, but we're going to need the ranges to answer any questions. Ranges vary from lab to lab, and results are meaningless with out the range of the lab that did the analysis. :)


Your results seem very up and down. Have you had any tests for thyroid antibodies, TPO and TgAb. If you have raised antibodies then flare ups can lead to up and down symptoms. If you are positive then I would strongly suggest you try a gluten free diet to help control/reduce the antibodies and symptoms.

1 like

Unfortunately, as greygoose has stated, Ranges are needed in order to respond to questions, due to the fact that labs use different machines which have different ranges, just to complicate matters.

Always request a print-out of your results for your own records and you can post if you have a query. Ranges are usually always included.

Most doctors think it is easy to diagnose hypothyroidism, just by looking at a TSH result, but this isn't the case. The TSH doesn't reveal all and sometimes it doesn't rise sufficiently to be diagnosed - UK is the worst of all in that other countries diagnose when TSH is 3+ but UK states that 10 is the magic number which is ridiculous if symptoms are disabling. Doctors, in the present day, appear to know no clinical symptoms at all.

What dose are you taking at present as I looked at your previous post and you were then taking T3 only (that's why your T4 would be low) but you were considering taking T4 added to T3.

It would be helpful to know exactly what dose(s).

It is a very anxious time when we've been diagnosed and feel awful but then there is a struggle to get to a dose which makes us feel well. That can take a few months at the very least as it isn't quite like taking a paracetamol for a headache (that would be good if it did happen).

I see also this occurred after you had a baby, which is a common occurrence so you have two things to consider, a new baby who needs to be looked after and not easy when Mum has no energy and feels awful..

Once you get into the hang of taking thyroid hormones (either when you get up or last thing at bedtime. If bedtime dose is preferable, you'd have to allow at least 2.5 hours gap between food or 3 hours if protein is taken. Food interferes with the uptake of thyroid hormones.

I assume you've been told to allow a gap of 24 hours between last dose of hormones and the blood test and take afterwards. If you decide on a bedtime dose miss this and take after test and at night as usual the same day.

Never accept the word 'normal' 'o.k' 'fine' with regards to blood tests, particularly when we don't feel normal. The blood tests do not inform the doctor of how bad or good we feel. it is only the patient who knows this and the aim is to return us to good health.

If you are due another test in about six weeks ask for TSH, T4, T3, free T4, Free T3 and antibodies (if you've not had antibodies checked). B12, Vit D, iron, ferritin and folate.

It can be a slowish road to wellness but it is good when you get there. Your FT3 looks very low and T3 is the driving force for all of our receptor cells.


Without ref ranges no one can tell


Oh sorry. I forgot the reference ranges.

And to answer one of the post, these tests were all done before I was medicated with t4 or t3.

And I was tested for TPO's and it was negative, less than 9.

Tsh range .5 - 5.0

Ft4 .8 - 1.8

Ft3 2.3 - 4.2


I would say you are undermedicated. Both are low in the range so ask for a increase. Just something to bear in mind. You can only test for bad conversion if you are of Levo so forget about adding T3 until we can definitely rule out that is a problem.

B12, folate, ferritin and Vit D aid conversion so could be helpful to get those tested anyway though in range is t good enough so post results, ranges and any suggestions from doctor about those as well as they can get rid of lingering symptoms you may have.


Yeah, FT4 bottom of range Ft3 under range - how can that be "normal"? And still rock bottom in the next test


Silverfox7, what did you say i could only test for if on Levo?


Poor conversion can only be tested for when on Levo only. Once T3 is added you can't tell how well you convert.


Makes sense. When you have a moment can you read the post I just finished please and let me know if you have any tips?


When on Levo only you can test TSH, FT3 and FT4 and if FT4 is high in the range and FT3 is low then your have a conversion problem, high FT4 as it's not converting well to the FT3 so that is low in the range.

When on any form of T3 the results are read differently. TSH will be suppressed as you are getting plenty of T3, FT4 can fall to halfway down the range as it doesn't hold onto a lot as it doesn't need to make a lot of T3 as it realises T3 is being provided and the FT3 should be high in the range.

Before conversion was decided my the difference in the FT3 and the FT4 readings but this time only the FT3 is accurate and the FT4 can fall in the range so that figure isn't accurate. It might fall a little or it might fall a lot so you have no comparison.


Hi I e just tried to answer your last question and I must confess one too tired to take it all in but correct me if I'm wrong but I'm getting the impression you are trying to get a text book figure for your TSH? If that is the case and my apologies if I've missed the point but never should any diagnosis be done on the strength of the TSH unless it's suddenly risen! For many of us the TSH is very inaccurate once on medication


Thanks Silverfox7. You totally answered my question.

I guess my main concern is stopping the t3. I have already reduced my original 18.5mg dose by 6.5mg's after I was on the t4 for two weeks. And I want to drop the t3 another 6.5mg's this week, but I'm feeling fatigued and I don't know if it's from the original drop in 6.5mg's from last week. I dont know if it's normal to be tired like this when transitioning because my ft4 is having to play catchup now that im taking less t3. Im hoping that gradually my energy will return once my ft4 catches up and converts to ft3. But I won't know unless I continue to decrease the t3. I hope all that made sense. I'm so frustrated with all of this and wish someone had just started me on t4 first to see if I would convert it. Now I have to play catchup and feel like crap (AGAIN) as I transition, then wait and see if I convert. Am I making sense?


Making more sense than I did last night-I was so tired!


You may also like...