Odd blood test results - TSH normal, FT4 high.

[Bananagal]

Hi all.

Hoping for some insights on a recent set of medichecks bloods I had done. I was primarily testing for vitamin and mineral levels as I am breastfeeding at the moment, and being lactose intolerant I worry about getting enough calcium and Vitamin D (incidentally all fine bar slightly low Vit D levels). However, I also got TSH and FT4 tested as there is a strong family history of hypothyroidism (both grandmothers and my Mum) and I do suffer from fatigue and low energy (probably no surprise with 2 kids).

These were the results:

TSH 1.26 (range 0.27 - 4.2)

FT4 25.6 (range 12 - 22)

A year ago I had the same test with the same ranges, and my results were normal (TSH 1.05, FT4 20.21). Antibodies and FT3 all normal too (I didn't test those this time.)

Clearly these suggest that I may be developing hyperthyroidism if anything, but I can't find any info anywhere on what it means when your TSH is normal and FT4 high? I don't really have any symptoms bar the tiredness and being a bit warmer than usual - but I had that last time I breastfed too. Shouldn't I be anxious, slim (ha!) and full of nervous energy?!

Any ideas? My GP just said, "your TSH is normal, you're fine. I wouldn't worry unless you start feeling ill." She's probably right, but I'm curious - any ideas what could have caused this odd result? I may check again in 6 weeks or so just for peace of mind.

Thanks!

[greygoose]

You really should have retested your FT3. That completes the picture. Your TSH is actually a long way from developing hyperthyroidism. But you can't really know anything for certain without the FT3, I'm afraid.

[Bananagal in reply to greygoose]

Yes, I will get a full set again next time I think. Unfortunately the package I chose this time only included FT4 and TSH. Hopefully FT3 will offer some more insight...

[greygoose in reply to Bananagal]

I'm sure it will.

[jimh111]

It could suggest mildly impaired deiodinase due to e.g. selenium deficiency, this would be accompanied by a low fT3.

However, your thyroid hormones are most likely normal. These are 95% reference intervals. i.e. 95% of the healthy population with have TSH or fT4 or whatever, that falls within the intervals. So, 5% of healthy people will have a result that is outside of the interval. The most likely reason is that your fT4 just happened to be a little above the upper limit of its reference interval, you were one of the 5% on this occasion.

[Hidden]

Hi, are you taking Biotin (vitamin b7)? Or a multivitamin with it in? If yes this can skew your results and you could stop taking it a week or so before the test. 🙂 but a full picture would only be had with having your t3 tested. Good luck with everything x

[Bananagal in reply to Hidden]

Thanks - yes, I take a breastfeeding multivitamin with 150 ug of biotin in it. That may explain it, thanks!