Why is my FT3 level getting lower on a constant dose of Levothyroxine?

[BreifneKing]

Reposted due to lack of response:

I am hoping that someone can offer an explanation for a fluctuating FT3 level, despite good levels of FT4.

Could it be solely down to conversion?

When I was taking 237.5mcg of Levo I was tempted to raise the dose but then figured that as my FT3 level at that dose was not too dissimilar to when I was taking 212.5mcg, I would revert to the lower dose and give it a bit more time.

As you can see below, my FT3 level was initially higher at the lower dose (May 2022) but then dropped 20% (July 2022):

November 2021 - 212.5mcg Levothyroxine:

TSH - <0.01 (0.27 - 4.20)

FT4 - 16.00 (9.00 - 19.00) 70% of range

FT3 - 5.00 (2.4 - 6.0) 72.22% of range

January 2022 - 225mcg Levothyroxine:

TSH - <0.01 (0.27 - 4.20)

FT4 - 17.10 (9.00 - 19.00) 81% of range

FT3 - 4.90 (2.4 - 6.0) 69.44% of range

March 2022 - 237.5mcg Levothyroxine:

TSH - <0.01 (0.27 - 4.20)

FT4 - 19.00 (9.00 - 19.00) 100% of range

FT3 - 5.20 (2.4 - 6.0) 77.78% of range

May 2022 - 212.5mcg Levothyroxine:

TSH - <0.01 (0.27 - 4.20)

FT4 - 16.20 (9.00 - 19.00) 72% of range

FT3 - 5.60 (2.4 - 6.0) 88.89% of range

July 2022 - 212.5mcg Levothyroxine:

TSH - <0.01 (0.27 - 4.20)

FT4 - 16.80 (9.00 - 19.00) 78% of range

FT3 - 4.50 (2.4 - 6.0) 58.33% of range

[radd]

BreifneKing,

Because when we surpass our sweet spot we start converting to other inactive thyroid hormone forms.

Remembering no hormone works in isolation it can take a while for labs to be seen & then effects to be felt. For instance it could have been your March 2022 where FT4 reached 100%, up-regulating D3 enzyme that not only converts FT4 to RT3 as a safety measure but will congruently convert FT3 to an inactive form of T2 whether T3 is high or not.

You do not have an unanswered post within ThyroidUK.

[BreifneKing in reply to radd]

Hi radd,I think 212.5mcg is my sweet spot so do I just sit tight or is there some way to ‘reset' enzyme activity or the conversion process?

[radd in reply to BreifneKing]

BreifneKing,

It’s not just a case of getting thyroid hormone levels right but ensuring they work effectively by optimising the cofactors; Vit B12, folate. Vit D and importantly iron. If these are low they could impact on your thyroid hormones workings and make you feel hypothyroid even if levels are right.

T3 results will also fluctuate if blood tests aren't like-for-like as spikes quicker having a shorter half life.

[BreifneKing in reply to radd]

Hi radd,My vitamin levels are all in order (and I supplement with Vit D, and B Complex to ensure they stay that way) and ferritin hovers around 100ng/mL.

Blood tests are always like for like - 8.30am and 24 hours after last dose.

So what would you suggest regarding enzyme activity / conversion?

Would it help to stop taking levo for a few days?

[Buddy195 Administrator]

How are you feeling on your current Levo dose? Have you any adverse symptoms? Sweet spots of optimal dosage vary for individuals and can vary over time, so it’s an ongoing challenge for many of us with thyroid conditions.

[BreifneKing]

Up until May, I was having the odd day where my head was a bit cloudy, and that didn’t change on a higher dose. Since May my brain fog has been getting progressively worse and I tend to run out of energy by late afternoon.

[Buddy195 Administrator]

Have you tested key vitamins (ferritin, folate, vitamin B12 and Vitamin D)? Having these optimal supports thyroid health. However, please don’t supplement before testing levels first.Taking a good B Complex (eg Thorne Basic B) improved my energy levels.

[BreifneKing]

Yes, vitamin levels are good.

As my TSH only became suppressed when I was on NDT, is it likely to increase now that I am on Levothyroxine, and therefore conversion may improve over time?

[mstp]

That is quite a high dose of Levothyroxine. Could it be that your body isnt converting the T4 to T3 as well as it should? This might explain the brain fog.

[BreifneKing in reply to mstp]

Hi mstp,

I am not altogether sure as the conversion rate on a slightly lower dose was worse when compared to the pre-July results:

September 2021 - 200mcg Levothyroxine:

TSH - <0.01 (0.27 - 4.20)

FT4 - 14.10 (9.00 - 19.00) 51% of range

FT3 - 4.60 (2.4 - 6.0) 61.11% of range

If it helps, before I was switched to NDT I was a lot less active than I am now and my blood results were as follows (note ranges were different):

October 2017 - 175mcg Levothyroxine:

TSH - 0.849 (0.27 - 4.20)

FT4 - 16.90 (12.00 - 22.00) 49% of range

FT3 - 5.70 (3.10 - 6.80) 70.27% of range

December 2017 - 200mcg Levothyroxine:

TSH - 0.148 (0.27 - 4.20)

FT4 - 19.40 (12.00 - 22.00) 74% of range

FT3 - 6.38 (3.10 - 6.80) 88.65% of range

February 2018 - 200mcg Levothyroxine:

TSH - 0.05 (0.27 - 4.20)

FT4 - 19.20 (12.00 - 22.00) 72% of range

FT3 - 5.73 (3.10 - 6.80) 71.08% of range

April 2018 - 200mcg Levothyroxine:

TSH - 0.04 (0.27 - 4.20)

FT4 - 17.7 (9.00 - 19.00) 87% of range

FT3 - 4.90 (2.6 - 5.7) 74.19% of range