Is conversion status solely based on FT3?

Hi All,

Is a person with low FT3, a poor converter, or are there other criterion? What are the factors that make a person a "poor converter"? Clearly if a person has a high FT4 and low FT3, they're likely not converting well. But if a person has a modest let's just say for hypothetical, FT4 1.13 (.82 - 1.77) with a low FT3, does this mean poor conversion is at play? Couldn't it be that this patient doesn't have enough FT4 and needs more t4?

What say you???

Thank you for your time, All.


21 Replies

  • Low vitamins, especially likely with Hashimoto's, and DIO2 gene variation would all affect conversion. So apparently does gut bacteria too.

    See this video

  • Thank you SlowDragon, I will take a look.

  • SlowDragon, you also reminded me, I need to look up DIO2 gene variation. So much to read! Thanks again! I will look at that link ASAP. 😊

  • Easy test to do. Worth it in my view, but then it underlined why I need T3

  • Your example would suggest undermedicated if both low but I sometimes advise to increase medication then check once stable that conversion is good. But because you are comparing the FT4 and the FT3 then that is why you can only check that if on Levo as on any form of T3 only the FT3 reading is accurate.

  • Thank you Silverfox7....yes, that was the question, whether a "normal" or midrange FT4 and low FT3 would indicate conversion troubles, but I neglected to state, and meant, before thyroid meds are ever started.

    I was told I was a poor converter. However, the private doc, the very first who diagnosed me as Hashimotos/hypothyroiditis and who gave me the NDT, HE never said that; only subsequent docs. At diagnosis, He only tested my FT4, TPOab, and something called the TRH. He did an ultrasound as well, and a physical of my throats and heel reflex. He diagnosed Hashsis and hypo thyroiditis and prescribed 1/4g NDT without instruction.

    Now after being on very low yet consistent (titrated every 7 - 12 days, each at 1/4g) dose of NDT for 8 weeks or so, my FT4 as we expect with NDT, went down to .90 (.82 1.77), FT3 2.4 (2.0 - 4.4). The rT3 lowered to 12.5(9.2 - 24.1), from 14.8.

    I'm getting retested bc that lab wasn't done fasting or early morning and may be skewed.)

    Assuming those labs are good, it appears that perhaps I never had enough FT4 available?

    Thank you so much....very much appreciated.

  • I'm not sure the term 'poor converter' is applied to someone not on medication. It primarily refers to a person who is not or cannot do well on T4-only, and I don't think you can tell from their pre-medicated results, only from trial and error.

    We can imagine a person who seems relatively healthy and has a healthy thyroid and pituitary, but has some problems downstream with using thyroid hormone, like conversion or transport into cells. But people don't get diagnosed with this at present. People who are diagnosed hypo have Hashimoto's, or Central Hypo. So in that case your big problem is that you don't have enough hormone in your body, the issue of conversion isn't an issue at that point. I'm not sure a person would have a problem converting their own hormone, as it seems more likely the problem is to do with synthetic hormone.

    Now that you're on NDT it shouldn't matter whether you're a poor converter, as NDT is ideal for poor converters. It contains a generous percentage of T3, and is in a slightly easier to process format.

  • Thank you silveravocado! I just saw this reply. Yeah, I didn't know really what the docs meant by poor converter - I wasn't yet in medication. But then I kept hearing the term....your explanation is quite helpful and thought provoking....thank you!

  • Yes there has to be enough FT4 in your blood for your body to convert enough to FT3. The blood test results for someone who is a poor converter would be FT4 high in range or over and FT3 low in range or under. Even then it would be worth getting the vitamins and ferritin checked - experience seems to show that low levels can cause poor conversion.

  • Hi eeng, thank you for your I wonder if ever I was a poor converter. Thanks again, very helpful.

  • As diogenes has explained in the past, we often need to take what medics consider "too much" T4 to get relief from symptoms when only on T4. (As our bodies are not designed for just T4)

    If, after correcting low vitamins and looking at food intolerances (usually gluten) and lowering antibodies there are still issues, then look at RT3 and adding T3 (or NDT) is next step

    If high T4 results in high RT3 then many need to lower T4 and add T3 (or NDT) instead

    NHS don't even test for reverse T3. Or often even test antibodies or FT3, or vitamins, or consider gluten so no wonder so many struggle to get correct treatment

  • I've seen people quote an actual ratio, but not sure I remember what it is... That T4 should be 4:1 or something of that kind. Maybe 3:1, and they gave a figure for what kind of ration implies it's not working.

    Unfortunately I don't remember who that was, or exactly what the ratio was. And also it probably won't work in the units you've got, which may be American ones? We're used to a reference range more like 11-22 for freeT4. From memory I think this is pmol/L

    I don't consider myself to know much about it, but I'd generally think of a conversion problem to be having a large gap between where those numbers appear in the range. So as you're saying, a mid-range freeT4 but a low I'm range or lower freeT3 suggests low conversion. But this would also be fairly undermedicated, people on T4-only often need a very high freeT4 in general.

  • Thank you SilverAvocado....thank you for replying. Yes I have seen many charts that show different examples of low this versus high this....but I hadn't seen anything regarding midrange FT4 with low FT3. That seems like a combo that only time and meds would tell a fuller picture of whether the patient is converting or simply doesn't have enough FT4.

    I'm glad I started on NDT then, because that little t4 in it may be helping me. I never took straight t4, but almost did. Tried straight t3, but just felt dried out (hair eyes overall). I didn't try anything for longer than three weeks. But I've been on NDT for now 8 weeks or so, just now getting up to 1.5g, so we will see once I get another blood draw.

    Thank you for your reply, it helps me think this all through so I can find the best approach.

  • TappedOut, see my reply to another post up the thread. Being a poor converter only really applies to people on T4-only medication. You can't really see it before you start the medication. It only matters when you're trying to tune medication.

  • I was given T4: my FT4 went up but my FT3 did not move up withit at all. So we knew I did not convert: then more T4 given should have meant an increase in FT3 too..

  • Thank you veraka....that makes sense. I have never taken straight t4, but before I took any thyroid meds at all, my FT4 was ok but not in optimal range. Yet I was told I was a poor converter.

  • If your thyroid was working OK, then you couldn't tell if you were a poor converter by the body tissues or not. The reason is that the thyroid will make up for the poor body conversion by producing more T3 direct. Only when this source is absent could you tell what level of body conversion you have from T4 offered.

  • TappedOut,

    You may be a poor converter if you are taking Levothyroxine only and have low TSH, high in range FT4 and low FT3.

    If you have TSH >1.5, mid-range FT4 and low FT3 you are undermedicated.

  • Hi there Clutter! Thank you... yes I was midrange FT4/low FT3 at diagnosis. I've been taking NDT for 8weeks now, looking to see an improvement. I'm still titrating up (just now got to 1.5g two days ago). I hope the little boost I needed on FT4, as well as thevirgent boost in FT3 that I need will be delivered via NDT, and my working on minerals (iron, i.e.).

    Thank you so much for your reply.

  • Hi T.O., your adrenal gland has a lot of input as well. If for some reason your adrenals are working too hard, they raise reverse T3 and block FT3 to put it simply.

  • 🤔🤔🤔Thank you Heloise! I know I need to get on the adrenals ASAP. I wished I woulda started with adrenals before taking any thyroid medications. Thank you! This helps.

You may also like...