What could cause both Free T4 and TSH rise? - Thyroid UK

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What could cause both Free T4 and TSH rise?


Someday in last August, I woke up at 2am with irregular heart rate and was diagnosed afib. In the blood test, it shows Free T4 was 1.78 ng/dL (normal 0.89-1.70) , and TSH was 2.692 mUnit/L (normal 0.55-4.78).

I happened to have a blood test in the same hospital four days before the afib, and by that time, my Free T4 was 1.58 ng/dL, and TSH was 1.270 mUnit/L.

Any idea what could cause both Free T4 and TSH rise? Thanks!

17 Replies

They can vary depending on time of day of test and recent activity too

TSH is typically higher in morning than afternoon

li17 in reply to SlowDragon

The test I got with afib was at about 3:45 am.

The other test four days ago was at about 3:50 pm.

shawsAdministrator in reply to li17

The TSH is highest early a.m. and drops throughout the day but am sure doctors/endos seem to be unaware of this. If our TSH goes too low they assume we're on too much levo. If in hospital we have no control over when they test, particularly if hypo and on levo. They seem to only test TSH and T4.

I would have a fresh FT4 and FT3 privately as NHS rarely test these as the doctors seem to be informed that a TSH gives the whole story.

I assume you know to always get the earliest possible test, fasting (you can drink water and allow a gap of 24 hours between last dose and test.

T3 is very important as it is required in our millions of T3 receptor cells which drives our metabolism. The heart and brain requirethe most and I know my heart played up before and after diagnosis.


Are you in UK?

For full Thyroid evaluation you ideally need TSH, FT4, FT3, TT4, TPO and TG antibodies, plus vitamin D, folate, ferritin and B12 tested

Essential to test antibodies and vitamins

Ask for magnesium to be tested too

If antibodies are high this is Hashimoto's also called autoimmune thyroid disease and can cause palpitations, irregular heart beat, and TSH levels to vary

See if you can get full thyroid and vitamin testing from GP. Unlikely to get FT3

Private tests are available


Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have money off offers.

All thyroid tests should ideally be done as early as possible in morning and fasting. This gives highest TSH and most consistent results. (Patient to patient tip, GP will be unaware)

Link about antibodies


Link about thyroid blood tests


List of hypothyroid symptoms




li17 in reply to SlowDragon

I'm in the US. None of my primary doctor, cardiologist or EP care to test my thyroid. Even I insisted it, they order incomplete test, so I don't have the full picture. Seem I need to get a good doctor first.

As you are vegan I am wondering about your levels of B12 - Folate - Ferritin - VitD. If they are low in range you can suffer AF. Also you need to know your FT3 result - if too low or too high AF can follow.

li17 in reply to Marz

I'm not vegan anymore after afib. I resume my previous diet. I did another blood test two weeks after first afib ,FT3 was 2.8 (normal 2.3-4.2). Vitamin D was within normal range but at the low side. Not sure about B12, folate and ferritin. Can these three be tested through blood draw? I may want to do another blood test.

Marz in reply to li17

Yes it is a blood test for B12 - Folate & Ferritin. B12 needs to be over 500 and Ferritin and Folate mid-range.

Your FT3 is very low in range and could be the cause of your AFib. When I started taking T3 my heart would tell me when the next dose was due. Google Low T3 syndrome and the heart :-)

Do you have the actual result for the VitD - ? VitD is also involved in heart activity ....

li17 in reply to Marz

Thanks! V D was 33 (normal 30 - 100). I've started taking vitamin D supplement about a month ago. The most recent blood test in December shows my Free T4 was 1.6 (normal 0.8 - 1.8), TSH 1.25 (normal 0.40 - 4.50), Free T3 3.2 (normal 2.3 - 4.2).

Could sudden change to full vegan diet cause low Free T3 and hight Free T4? I'm so confused by these thyroid data. And my doctors just don't care to find out the cause of my afib but sent me away with heavy meds (I didn't take them though).

SlowDragonAdministrator in reply to li17

It must be easier in USA to get private testing

Essential to test both TPO and TG thyroid antibodies

Low vitamin B12, folate, ferritin and vitamin D can all affect thyroid

If you were vegan and not supplementing B12 that's likely low


The Thyroid Pharmacist, Amy Myers, Dr K news, Chris Kresser, Dr Mark Hyman

All USA based thyroid specialists

Functional medics will look for cause, not symptom. Vitamins are important

Good you are supplementing Vitamin D. Look at magnesium and vitamin K2 Mk7

Loads of posts on here about this

li17 in reply to SlowDragon

I asked couple labs if I can order my own test and pay out of pocket, they didn't allow me but said I have to get my doctor to order the tests. Maybe I haven't found the private lab.

I do need to find a functional doctor to help. The traditional docs just don't care. Thank God I didn't start the heavy med for afib.

Marz in reply to li17

Your VitD neeeds to be around 60 - so how much is in your D supplement ?

Your LOW FT3 could be caused by poor conversion from T4 which is a storage hormone - into the ACTIVE hormone T3 - which is needed in every cell of your body. Including the cells of your heart - so when T3 is low in the blood there simply is not enough to go around the whole body !

So if you have LOW B12 - Folate - Ferritin - VitD - you will have poor conversion of T4 into T3.

Ferritin is stored iron in the liver - so if LOW you will need to have a FULL IRON PROFILE done - anaemia can also be the cause of AFIb - as the heart beats faster when oxygen is low in the blood. Iron clings to the red blood cells - Oxygen clings to the Iron to be circulated around the body. Low Iron = Low Oxygen = increased heart beat in an effort to produce more oxygen. My simplistic non-medical explanation :-)

SlowDragon has given you some good people to read about and learn. Sadly most of us who have found wellness have done so by ourselves - reading .....and reading and taking action. Also keep asking questions here and people will help.

Please try to remove the word normal from your thoughts - what is normal for you is not normal for me. Ranges are just that - ranges. It is where you are in the range that is key to your wellbeing. Docs use the word normal - after all we all want to be * normal * ......

Did you google Low T3 syndrome and hearts ?

li17 in reply to Marz

Thanks for the detail explanation. Now I can see a trail that could possibly cause my afib. I suddenly switched to vegan diet about 12 or 13 days before my first afib. Right after that, I felt very tired for 3 or 4 days, and had diarrhea for few days, along with heavy sweating when I was sleeping. I didn't pay enough attention to the symptoms, and didn't take any supplement, I was thinking to just try it for two weeks and see if I would feel better. Now it seems like the vegan diet caused B12, Vit D and probably Folate and Ferritin deficiency, hence caused thyroid problem then my afib.

Not sure if this sounds reasonable/correct. I'm pretty sure if I tell the above to any of my docs he will just dismiss me. Actually one of my cardiologist thought I have mental disease by keeping asking similar questions...

Marz in reply to li17

Please follow the advice and have the FULL thyroid check to include the anti-bodies already mentioned TPO & Tg. If they are within range then you can rule out Hashimotos - which is an auto-immune condition and the most common of thyroid issues globally. So without the tests how will you or any Doc know ??

I really do not think your Vegan diet would have trashed your Vitamins and Minerals so quickly - it could have been creeping up slowly. Why did you necome Vegan - ? Perhaps you were feeling poorly and thought it would help.

You forgot to tell me the amount of VitD you are taking :-) Also did you look up Low T3 Syndrome and hearts ?? :-)

Please read through your thread again - looking at the advice and make some notes - like a shopping list or Things to Do list ! Then tick them off when completed ....

li17 in reply to Marz

Yes I just looked up low T3 syndrome. I'm taking 5000 IU Vit D3 daily, I think my D3 level should be higher than December. I'm going to find a lab that would allow me to do private test, otherwise I can't get my docs to order all these tests.

You're right. I started vegan because I was feeling bad during last July and August. I was perfectly healthy before July. Then on July 6th, I had my first panic attack when I was working on my customer site. Probably because I drank too much black coffee and didn't have enough sleep that day. Since then I've been worrying about my heart. I tried to make an appointment with cardiologist, but the earliest availability was in late August. So during the time I was waiting for the appointment, my anxiety level kept going up and I started to try all I can to get my heart healthy. That's why I stopped all caffeine and alcohol and started vegan diet. To me I can see a trail that led me to afib, maybe the combination of these factors put me into afib. I'm feeling regret about not calming down and hoping by ruling out the cause and correcting it can help me get rid of afib. Being 37 yo with three very young kids, I want to get my life back so much.

I really appreciate your help, Marz and Slow Dragon, and other people that replied to me. Thank you!


It's possible your TSH was elevated due to the AFib. It is unusual for TSH and FT4 both to be high. As it happened while you were ill it may be a one-off. I would have TSH and FT4 retested after 4-6 weeks. If both are still high you will need to see an endocrinologist to investigate further. Resistance to thyroid hormone and TSHoma, a benign pituitary adenoma, are possible causes.

Contact the Facebook pages of Mary Shomon, Gina Nolen or Hypothyroidmom for information about labs where you can order your own blood tests.

li17 in reply to Clutter

Thanks. I’ll order the lab test.

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