Are FT4 levels important in thyroid function test?

[mellohealth]

I recently had bloods done privately by a company called Thriva for thyroid function and my TSH was in normal range but my FT4 was elevated and they suggested I contact my GP to discuss this with a view to adjusting my Thyroxine. My GP suggested doing another blood test and asking for FT4 test as well as TSH which we done but the lab only done TSH. After discussion with my GP she stated that she had spoken with the bio chemist and basically agreed with their statement that if the TSH is in normal range then FT4 is completely irrelevant and is not a marker for my thyroid function. Only if TSH is out of normal range will they then look at FT4. Can anyone clarify for me if this is correct as I have always believed that both TSH and FT4 levels should be in normal range?

[SlowDragon Administrator]

Please add actual results

Was test done early morning

Full thyroid test is TSH, Ft4 and Ft3 plus both TPO and TG thyroid antibodies

Important to test vitamin D, folate, ferritin and B12 as well

Get GP to test if these weren’t done by Thriva

[PurpleNails Administrator]

Many feel that unless FT3 the active hormone isn’t at a good level then they are unwell. Some manage with low FT4 levels & other need both FT4 & FT3 at a good level.

If your TSH is in range (should be under 2 better around 1 if taking replacement) it could mean you need of high or a fraction over range for it to be high enough to convert to enough FT3.

Was FT3 tested?

Do you have actual results & ranges?

Do you have a diagnosed condition? Taking replacement thyroxine? Taking just prior to sample can show a false high? How do you test. timings & did you eat it all can affect results.

Drs focus on TSH but it’s not 100% accurate.

Also important to test antibodies & nutrients were these tested too?

[greygoose]

Can anyone clarify for me if this is correct as I have always believed that both TSH and FT4 levels should be in normal range?

Despite what doctors think, the TSH is not that important. It's important if it's high - and by high I mean more than 1 for someone on thyroid hormone replacement - but once it reaches 1, it ceases to be of much use. Very often, people on thyroid hormone replacement need enough hormone to suppress the TSH. And if that is the case, so be it. You can only get the TSH back in range by sacrificing some of your dose, and with it your health, probably. It's not that important and should never, ever be used to dose by.

T4 is basically a storage hormone that doesn't do much until it's converte into the active hormone, T3 - which makes FT3 the most important number. But, the FT4 is important in that if it is low, you won't have much to convert, so your FT3 will be low, too. And, if it's high, but you don't have any symptoms that could be 'hyper'-type symptoms, or if you still have hypo symptoms, then you probably don't convert very well, and your FT3 will be low. But, to know how well you convert, you need your FT4 and your FT3 to be tested at the same time, and compare them.

Whether or not it's a bad thing to have your FT4 over-range hasn't been proved yet. There's some evidence that it might be a bad thing, but I don't know any details. So, the jury is still out on that.

But doctors don't know any of the above, because they don't learn it in med school.

[radd]

mellohealth,

Welcome to our forum,

No, it is not correct to only consider the TSH when medicating Levothyroxine but sadly how GP’s are directed to dose.

TSH decreases as thyroid hormones raise and healthy people usually present an accurate inverse correlation but in people with thyroid/endocrine issues where thyroid signalling can become skewed TSH can not be used as a reliable marker for assessing thyroid hormone levels.

Factors effecting TSH may include medicating T3, central hypothyroidism, resistance to thyroid hormone, recent/long term non-thyroidal illness, TRAb's even in the presence of Hashi, and for many of us a down-regulation meaning we will never manage to gain enough thyroid hormone unless TSH is allowed to remain under-range.

Knowing FT4 levels is also important to avoid over-dosing as taking levels higher in a bid to achieve enough T3 risks surpassing our sweet spot. The deiodinases are enzymes that control activation/deactivation of thyroid hormone, and are influenced not only by differing physiologic conditions but also the amount of thyroid hormone we medicate.

If more T4 is taken than the body can tolerate it will naturally convert to an excess of RT3 which not only deprives us of T3 but becomes counterproductive as will encourage meds to work against us. Because TSH promotes type-2 deiodinase in T4 - T3 conversion, this is when a small amount of added T3 is beneficial to compensate for the loss of conversion caused either by genetically impaired converting ability and/or a low TSH.

The only way of gaining a better picture of thyroid hormones levels is to measure TSH, FT4 & FT3.

[SlowDragon Administrator]

Last dose levothyroxine should be 24 hours before test

How much levothyroxine are you currently taking

Do you always get same brand levothyroxine at each prescription

Many people find different brands are not interchangeable

Bloods should be retested 6-8 weeks after each dose change or brand change in levothyroxine

Just testing TSH and Ft4 is completely inadequate

For full Thyroid evaluation you need TSH, FT4 and FT3 plus both TPO and TG thyroid antibodies tested.

Very important to test vitamin D, folate, ferritin and B12 at least once year minimum

Recommended on here that all thyroid blood tests should ideally be done as early as possible in morning and before eating or drinking anything other than water and last dose levothyroxine 24 hours before test

This gives highest TSH, lowest FT4 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

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 by DIY fingerprick test

bluehorizonbloodtests.co.uk...

If you can get GP to test vitamins and antibodies then cheapest option for just TSH, FT4 and FT3

£29 (via NHS private service ) and 10% off down to £26.10 if go on thyroid uk for code

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

monitormyhealth.org.uk/

NHS easy postal kit vitamin D test £29 via

vitamindtest.org.uk

Link about thyroid blood tests

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

Link about Hashimoto’s

thyroiduk.org/hypothyroid-b...

List of hypothyroid symptoms

thyroiduk.org/if-you-are-un...