Is there a formula or a link to work out the percentage conversion of T4 to T3? Past results are below.
I’m having a bit of a battle with my GP over my symptoms and want to present the conversion percentages to him. I’m currently on 100mcg of levothyroxine.
June 2020 GP Test No FT3
TSH 0.39 (0.27-4.2)
FT4 25.1 (12-23)
July 2020 Thriva test
TSH 0.03 (0.27-4.2)
FT3 4.4 (3.1-6.8)
FT4 26.3 (12-22)
May 2023 Randox test
TSH 0.142 (0.35-5.5)
FT3 3.65 (2.8-6.5)
FT4 25.6 (11.9-21.6)
Molly139
want to present the conversion percentages to him
Don't pin your hopes on your GP understanding about conversion, as far as most doctors are concerned if the result is within range then everything is fine. Most doctors don't understand the importance of T3 and don't realise it's the active hormone that is needed by every cell in our bodies.
To work out conversion rate of T4 to T3, as long as the unit of measurement is the same you divide the FT4 result by the FT3 result. Good conversion is said to take place when the ratio is 4:1 or less, over 4:1 suggests poor conversion.
From your results above:
July 2020 Thriva test
TSH 0.03 (0.27-4.2)
FT3 4.4 (3.1-6.8)
FT4 26.3 (12-22)
26.3 divided by 4.4 = 5.97
So a conversion rate of 5.97:1
May 2023 Randox test
TSH 0.142 (0.35-5.5)
FT3 3.65 (2.8-6.5)
FT4 25.6 (11.9-21.6)
25.6 divided by 3.65 = 7.01
So a conversion rate of 7.01:1
Quick question, what should the conversion percentage be?
No conversion percentage, you use the ratio as I said above, good conversion takes place when ratio is 4:1 or less.
got it 👍
Oh dear....a fairly common problem, a GP lacking knowledge of thyroid disease!
How many of the following symptoms can you tick off and present to this GP?
thyroiduk.org/if-you-are-un...
You don't only need a formula to identify poor T4 to T3 conversion.....just compare FT4 with FT3. If FT4 is high and FT3 is low in comparison then conversion is impaired.
That however doesn't answer the why....see below for this
Your labs show this to be the case and a medic should know this!
Note discrepancy between the Frees
July 2020 Thriva test
TSH 0.03 (0.27-4.2)
FT3 4.4 (3.1-6.8) 14% thro' ref range
FT4 26.3 (12-22) 143% ditto
May 2023 Randox test
TSH 0.142 (0.35-5.5)
FT3 3.65 (2.8-6.5) 22.97% ditto
FT4 25.6 (11.9-21.6) 141.24% ditto
(We use this %age calculator
thyroid.dopiaza.org/?utm_so...
Both sets of results clearly show poor conversion and therefore wrong medication!
However you must also address the essential nutrients
Vit D, vit B12, folate and ferritin which need to be optimal to support thyroid function/ conversion.....these are very possibly low.
Adding a little T3 ( say 5mcg initially) to your current dose of 100mcg should help raise FT3 and will in turn reduce FT4
There is no need to reduce levo at this point...and only ever change one dose at a time.
This can answer the why....
You could also have a genetic test to find out if your conversion is impaired by the Dio2 polymorphism. If this is homozygous ( inherited from both parents) the impact is greater than if heterozygous ) from one parent. I tested homozygous!
thyroiduk.org/deiodinase-2-...
academic.oup.com/jcem/artic...
Common Variation in the DIO2 Gene Predicts Baseline Psychological Well-Being and Response to Combination Thyroxine Plus Triiodothyronine Therapy in Hypothyroid Patients
I doubt your GP is fully conversant with T4/T3 conversion and clearly is struggling to analyse your labs
I suspect he only looks at TSH which is not a reliable marker
thyroidpatients.ca/2021/07/...
GPs cannot prescribe T3 so ask them to refer you to an endocrinologist on the grounds of your poor T4 to T3 conversion
Use the info above to then explain to the endo why you asked to be referred and that you would like to be prescribed a trial of T3 replacement.
Asking fo a trial rather than asking outright to be given T3 is a softer approach!!
At that stage you will probably need to come back here for more advice!
Any questions....just ask members for advice.
Good luck!
Thank you Dippydame for taking the time to help. I’ve not read it fully yet but can’t wait to gain more info on this flipping disease!
SeasideSusie helped me lots yesterday, I’m working on getting my vitamins top of the range, fingers crossed 🤞
Hope something there helps...you're welcome
Yes, SeasideSusie is a fund of knowledge....follow her advice.. She is one of TUK's experts who has helped me since I arrived here a number of years ago.
It all becomes clearer the more we learn.
The general lack of thyroid knowledge amongst medics beggars belief.
Good luck!
I really enjoyed reading your post thank you, lots of symptom boxes were ticked. As Susie suggested start to get top of the range scores in vitamins. I’ve ordered the Vit B complex that Jaydee recommended, I take 5,000iu daily Vit D plus vit K2-MK7 and magnesium. 2 weeks later I’ll add selenium.
Just looking back at my original post, no one commented about results for folate and ferritin, unless I missed it 🙈 Ferritin doesn’t look optimal but I’m no expert! Could I do anything to improve these?
Folate 11.6ug/L (deficient if < 3.9)
Ferritin 158ug/L (30-400)
Susie is much better placed than I am to give advice on nutrition
SeasideSusie ....thank you
Molly139
Folate 11.6ug/L (deficient if < 3.9)
Ferritin 158ug/L (30-400)
I mentioned in reply to yesterday's post the following:
Folate: at least half way through range
Ferritin: half way through range although some experts say the optimal ferritin level for thyroid function is 90-110ug/L
Folate has many different ranges, sometimes with a lower and upper limit, sometimes just mentioning the deficiency level as yours does, ie <3.89 and in this case we suggest aiming for double figures. Yours is 11.6 so is OK, the B Complex you have ordered contains 400mcg methylfolate and that should at least maintain, and may even improve, your level.
As for Ferritin, again this has many ranges. The range for yours is actually the range usually used for males, the female range is often 13-150, can be 15-300 and if over 60 one lab uses the range 30-650. As a female you wouldn't necessarily aim for half way through your given range, and I've quoted what some experts suggest as the optimal level for thyroid function.
We have to remember that ferritin rises with inflammation so it's actually helpful if an inflammation marker is tested at the same time as ferritin, this doesn't happen with NHS tests but is often included in private tests and the test included is CRP. If CRP is raised then ferritin will show as a false high.
Your ferritin level is looking remarkably good for a hypo female, but unless CRP was also tested we don't know for sure if this is a true level. So the question is, was this a private test or NHS and was CRP tested as well?
It was an NHS test, unfortunately no CRP test. I’m 66 and female so looks like you’ve found an error with their ranges!
Not necessarily an error with their range, that's probably their normal range. There are so many ranges for ferritin it's totally confusing. The ranges I quoted above are mainly for the private labs. My NHS range for ferritin is 15-300 for everyone whereas the private labs have different ranges for males and females with the male range having a higher upper limit.
Just in case I confused you over percentages... I probably did!
The %ages I referred to in my reply are %age of the hormones ( FT4 and FT3) through. their respective reference range.... NOT conversion percentages
We aim to have those percentage levels roughly approaching 75%....as humans,not machines, we are all somewhat different!!
But if you look at your FT3 % ages through ref ranges (that I added above) you can immediately see the levels are far too low....14% and 22.97% are far from 75%
Similarly your FT4 levels are far too high....141.24% and 143%
That high FT4 v low FT3 difference indicates that T4 is not being adequately converted to T3
Susie's use of ratios is a more mathematical/ definitive way of coming to a similar conclusion....I avoid calculations if I can!! That's why I use the Thyroid Test Results Calculator that I added a link for and work from there.
Bottom line...
T3 is the active thyroid hormone and needs to flood nearly every cell in the body by way of an adequate and constant supply
Your T3 supply is far from adequate and probably not constant!
Low cellular T3 = poor health
You are going to benefit from added T3 even after you have optimised the essential nutrients.
But, one step at a time....as Susie advises, nutrients first!
Hope this ramble makes sense!
TSH after RAI treatment. 
Latest nhs GP blood test results - any help or advice appreciated
Blood results after adding T3
T4 to T3 Conversion
