Low TSH, Subacute Thyroiditis & Iodine Excess

[gemmerg]

I was diagnosed with hyperthyroidism at the end of January after a routine blood test following four consecutive chemical pregnancies. I've seen an endocrinologist and had a RAIU scan which has confirmed the cause as subacute thyroiditis, which in hindsight, I believe I had at the end of June 2022. Furthermore, in late August, I started taking prenatal vitamins, which contained iodine, and therefore unknowingly prolonged the thyroid inflammation. Since stopping the vitamins at the end of January, my FT4 normalised very quickly but TSH is still very suppressed:

13/02

FT4 - 23 (9-28)

TSH - <0.01 (0.23-5.6)

08/03

FT4 - 19 (9-28)

TSH - 0.03 (0.23-5.6)

I'm very impatient to start trying to conceive again given my age and other issues impacting fertility. My endocrinologist has said my next blood test is in another month which is feeling like a long time to wait to get another indication of how my thyroid is recovering. I'm struggling to find anyone else with similar cause of their hyperthyroidism but keen to get any views on how soon I can expect TSH to normalise? All thoughts welcomed.

[greygoose]

TSH moves a lot more slowly than thyroid hormone levels. It can take months to rise.

But, it's not the TSH that will stop you conceiving, whether it's high or low. It's the FT4 and FT3 that are important. They are the thyroid hormones. TSH is just a chemical messenger from the pituitary to the thyroid, telling it to make more or less hormone. But there are many, many things that can affect TSH levels - like time of day, for example - so that it is not a good indicator of thyroid status.

Your latest FT4 is just a tad over mid-range, which is good. It would be nice to know what the FT3 is like, though. And, have you had your antibodies tested?

[gemmerg in reply to greygoose]

Thanks greygoose. My endocrinologist advised waiting to start trying again until TSH and FT4 had been in the normal range and stable for two consecutive months, which feels like a very fluid yard stick at this stage. I believe there is also a chance I could go underactive as part of the recovery process, which could end up being permanent. I haven’t had FT3 tested since the initial test where it was in the upper part of normal but my antibodies are negative. Given TSH had started to rise at my last blood test, is that an indication that things could move reasonably quickly now or does it not give any indication of rate of change?

[greygoose in reply to gemmerg]

As I said above, it doesn't give much of an indication of anything at all. But, TSH will doubtless rise as FT4 drops. And if you're going to get pregnant you don't want your FT4 any lower that that. I very much doubt that your endo is that clued up on the subject. You need one that specialises in pregnancy.

And, as I also said, TSH levels depend on the time of day you have your blood draw. Do you always have them at the same time? What time?

You cannot rule out autoimmune thyroiditis on the basis of one negative antibody test, because antibodies fluctuate all the time. And, also because there are two tests that should be done, but the NHS only does one of them. And, furthermore, not all people with autoimmune thyroiditis have high antibodies. They are diagnosed by ultrasound. Was anything said about autoimmunity when you had your scan?

I believe there is also a chance I could go underactive as part of the recovery process, which could end up being permanent.

Yes, you could - and it could. If you have AIT.

Do you know the link between hypothyroidism and pregnancy? To get pregnant in the first place, you need good levels of T3. T3 is the active hormone needed by every single cell in your body to function correctly. If there's not enough, you will get all sorts of symptoms, including the inability to conceive.

Once you have conceived, you need good levels of T4 to 'nourish' your baby until s/he develops their own thyroid around the end of the first trimester.

But, the TSH has nothing to do with any of that. So, don't let them fob you off about the TSH needs to be this that or the other. It doesn't. It's the thyroid hormones themselves they should be looking at.

[thyroid012 in reply to greygoose]

greygoose,

Always TSH and FT4 tested when ttc and then pregnant as radd said TSH very important as does other things with pregnancy hormones. TSH has to be low and not high I had miscarriages because mine was high.

[radd in reply to greygoose]

gg,

'But, it's not the TSH that will stop you conceiving, whether it's high or low'

Low TSH is ok but high is not.

Not only because it is generally representative of inadequate thyroid hormone for conception but because prolactin correlates with TSH. High prolactin prevents the release of the egg from the ovary. Hence it is possible but difficult to get pregnant whilst breastfeeding.

'But, the TSH has nothing to do with any of that. So, don't let them fob you off about the TSH needs to be this that or the other'.

Conception and pregnancy is one time TSH is of vital importance. Especially as the O/P is not medicating replacement, it is essentail she has a normalised TSH response to achieve enough hormone.

After conception hCG will encourage more thyroid hormone alongside TSH but increased oestrogen will raise TBG binding capacity. Early TFT's can be challenging and both TSH and thyroids hormone levels are always viewed to ensure enough thyroid hormone for pregnancy retention.

[radd in reply to radd]

 gemmerg

This is not wholly relative to you because you are not medicating thyrodi hormone replacement but the majority might be helpful as is an interesting read.

Tips to help raise TSH. ... thyroidpatients.ca/2020/01/...

[gemmerg in reply to radd]

Thanks so much h for sharing. I'm definitely ticking the sleep deprivation box anyway, thanks to my three year old😀

[SlowDragon Administrator]

Meanwhile strongly recommend getting FULL Thyroid and vitamin testing done privately

Quite likely low vitamin levels

all thyroid blood tests early morning, ideally just before 9am

This gives highest TSH, and most consistent results. (Patient to patient tip)

Private tests are available as NHS currently rarely tests Ft3 or all relevant vitamins

List of private testing options and money off codes

thyroiduk.org/getting-a-dia...

Medichecks Thyroid plus antibodies and vitamins

medichecks.com/products/adv...

Blue Horizon Thyroid Premium Gold includes antibodies, cortisol and vitamins

bluehorizonbloodtests.co.uk...

Only do private testing early Monday or Tuesday morning. 

Link about thyroid blood tests

thyroiduk.org/getting-a-dia...

Link about Hashimoto’s

thyroiduk.org/hypothyroid-b...

[Cwbsi]

I had subacute thyroiditis a few years ago though my clinical case was very different to yours