Question about TSH

[ERIC107]

Hello wise people!

I have a question that is more out of curiosity than concern. I am aware that the TSH level is a somewhat minor piece of information in the process of finding suitable dosing to treat AITD, and I also know that the measured values can be quite variable from test to test.

All that being said, I'm curious about the mechanism behind my gradual drift upwards in TSH values since starting to take 25 mcg of thyroxine. Does anyone know the potential reason behind my TSH blood results posted - shown in my *new* "thyroid spreadsheet" (I LOVE a good spreadsheet!)? My GP obviously panicked when she saw the TSH increase when the lab, weirdly, looked at my TSH and T4 levels - they were only supposed to be doing B12 and folate levels (only 4.5 weeks after starting thyroxine) and texted me immediately instructing an increase to 50 mcg.

In case the spreadsheet screen grab is too tiny to see easily, the relevant numbers are:

24 May 2023: GP test (not yet taking thyroxine, 11:00am, only water before)

TSH = 5.77 (0.20 - 4.50), 128.2%

FT4 = 10.2 (7.0 - 17.0), 32%

FT3 = not measured

06 July 2023: GP test (25 mcg thyroxine, last does >24 hours before, 9:35am, only water before)

TSH = 7.38 (0.20 - 4.50), 164%

FT4 = 10.2 (7.0 - 17.0), 32%

FT3 = not measured

10 July 2023: Medichecks (25 mcg thyroxine, last does >24 hours before, 9:30am, only water before)

TSH = 8.49 (0.27 - 4.20) 202%

FT4 = 16.2 (12.0 - 22.0), 42%

FT3 = 4.0 (3.1 - 6.8), 24.32%

Not worried at all - just puzzled/curious as I'm getting bogged down in the weeds of the data. Thank you!

[EDIT: Goodness... sorry - I didn't realise the pic would be that huge!]

[SlowDragon Administrator]

Standard STARTER dose is 50mcg unless over 65 years old

Very common for TSH to increase on only 25mcg

You will very likely need at least two further increases over next 6-12 months

Very very helpful profile

Which brand is the new 50mcg ?

guidelines on dose levothyroxine by weight

Even if we frequently start on only 50mcg, most people need to increase levothyroxine dose slowly upwards in 25mcg steps (retesting 6-8 weeks after each increase) until eventually on, or near full replacement dose

NICE guidelines on full replacement dose

nice.org.uk/guidance/ng145/...

1.3.6

Consider starting levothyroxine at a dosage of 1.6 micrograms per kilogram of body weight per day (rounded to the nearest 25 micrograms) for adults under 65 with primary hypothyroidism and no history of cardiovascular disease.

Also here

cks.nice.org.uk/topics/hypo...

pathlabs.rlbuht.nhs.uk/tft_...

Guiding Treatment with Thyroxine:

In the majority of patients 50-100 μg thyroxine can be used as the starting dose. Alterations in dose are achieved by using 25-50 μg increments and adequacy of the new dose can be confirmed by repeat measurement of TSH after 2-3 months.

The majority of patients will be clinically euthyroid with a ‘normal’ TSH and having thyroxine replacement in the range 75-150 μg/day (1.6ug/Kg on average).

The recommended approach is to titrate thyroxine therapy against the TSH concentration whilst assessing clinical well-being. The target is a serum TSH within the reference range.

……The primary target of thyroxine replacement therapy is to make the patient feel well and to achieve a serum TSH that is within the reference range. The corresponding FT4 will be within or slightly above its reference range.

The minimum period to achieve stable concentrations after a change in dose of thyroxine is two months and thyroid function tests should not normally be requested before this period has elapsed.

[SlowDragon Administrator]

Ferritin was tested in May and result is extremely deficient at 12

Will flag up to humanbean and SeasideSusie to comment on full iron panel results

Any obvious reason for low ferritin

Are you vegetarian or vegan?

Do you eat red meat

Are you post menopause

[ERIC107 in reply to SlowDragon]

Hi SlowDragon - many thanks for replying!

humanbean already replied to an earlier post I made about my original diagnosis and talked about the ferritin value. I'm already addressing my iron levels. 😊 (Incidentally, also my B12, folate, and Vit. D - to get them up towards optimal rathe than just "normal".)

To answer your specific questions... I am vegetarian and I am post menopause.

I've already gone up to 50 mcg (currently just doing 2 x 25 mcg Wockhardt but new prescription has been fulfilled with 50 mcg Teva tablets - forgot to check before leaving the pharmacy!).

Do you know anything about WHY the TSH goes up on a low dose of levothyroxine? I'm a scientist by training (analytical chemist) and I always like to know the "whys" and "hows" behind scientific data. I was wondering why the TSH is changing in the observed fashion. No worries if you don't - I'm trying to fill in all the background to this newly-diagnosed condition... just how my brain works.

[tattybogle in reply to ERIC107]

WHY the TSH goes up on a low dose of levothyroxine?

So it doesn't always.. in some people TSH will go down after a few weeks on a small dose of levo, (and then eventually go up again once their body recognises the small dose isn't enough )

~ so first you need to understand that TSH operates 'on bit of a delay'..... TSH is more like 'a window into the recent past' rather than 'what is happening today' ..... it lets you know what levels of thyroid hormone you had over the few weeks leading up to the test ,

~ whereas fT4 is a direct measure of the fT4 level in your blood today in real time.

So when you get a set of TSH / fT4 results .. they are not really looking at what is happening at the same point in time .

This is why there is a 6-8 week wait until we test bloods after any dose change, because it can take several weeks for the TSH level to start to react, move , then adjust itself , and then settle again at it's stable level for that particular level/ dose of thyroid hormone.

it's also a bit 'slow' to react to smaller/ more subtle changes in thyroid hormone level .

so in your case the most likely explanation for TSH currently being higher is that it's only 4.5 weeks since you started on a tiny dose of T4 ... so your TSH just hasn't noticed it yet (or rather your hypothalamus / pituitary haven't noticed it yet , they are what control the TSH level ,... but its easier to type TSH)

Warning ~ if you're an analytical scientist , trying to understand your own TSH / fT4 / fT3 results on levo ,may fascinate you and pi** you off , in equal measure .

TSH / fT4 (and fT3) will sometimes do completely inexplicable things ... and just when you think you've understood your own 'settings' and know what it will do ... it will do the opposite and leave you going ????

[ERIC107 in reply to tattybogle]

tattybogle - thank you so much for an exceptionally useful reply (I have found many of your detailed answers to other folks' questions incredibly well explained - you would make an excellent teacher/explainer (maybe you are/have been)!) The concept of a delayed response makes perfect sense to me. And also thanks for the warning re: data crunching and its potential to drive one mad 😊 I also, currently, only have three data points, which is better than two but nowhere near as good as five or more... so I'll hold my horses and practise patience.

[tattybogle in reply to ERIC107]

Thanks .. i'm like you , i need to see how the cogs of something actually work. i've worked with kids in various capacities from nanny to bus driver cum dinner lady cum kindergarten assistant ... but i've never taught anything 'officially' ... i'd get struck off for going rogue and teaching em how to drive the bus up the school track .

my TSH made very little sense when i started on levo ;

it was 6.8 before levo .

i took 50mcg for 7 weeks and it was 2.9 ,

i took 100mg for 5 months and it was 2.5 ,

i took 150mcg for 3 months and it was 2.7 .

i took 150 for another 8 months then , 175 for a month ... and it was <0.001

??? ...... seemed to be 'stuck ' for year despite large dose increases .... i have concluded my TSH needs either a very long time and /or a massive kick up the a** , to persuade it to move. which will of course be proved wrong next time it try to second guess it .

with hindsight i wish i had a result for just before i increased to 175 , but i don't . The problem with relying on NHS testing is you wont have the most important bits of data eg. they have (amazingly) tested my fT3 on about 5 occasions over 20 yrs without me asking , but not when i was actually having symptoms of overmedication (muppets) .. .... so if you want 'useful' data to analyse , best to do your own (TSH / fT4 / FT3 ~ same protocol every time ~ time of test, hours from last dose, fasting etc) and remember to do it before you make any changes as well as afterwards , then you may learn something useful.

[HealthStarDust]

That’s a huge difference in your FT4 levels just days apart.

[SlowDragon Administrator in reply to HealthStarDust]

different ranges on Ft4 tests…..percentage not much difference

[McPammy]

Your TSH may be increasing due to low T3. The TSH looks at T4 and T3 in your body. I think you need a full test to know exactly why your TSH is increasing. Even though you are on a smallish dose of levothyroxine and your T4 level is adequate you may be low in the most important hormone T3 and your TSH is high as it’s calling for more T3 to be made. You may be a poor converter of T4 to T3. I like a good spreadsheet too coming from the analytical world of supply chain and production planning.

[ERIC107 in reply to McPammy]

Thank you McPammy (spreadsheets FTW! 😂). I had wondered about T4 to T3 conversion... but I'm going to hold off from focussing on that too much *yet*!

[McPammy in reply to ERIC107]

Holding off may delay your understanding on why your TSH is increasing. You can’t know the reason of the increase without all three tested TSH, T4 and T3. It’s like knowing the answer to a sum without the formula.

[ERIC107 in reply to McPammy]

That's a good point, thank you!