Increased levothyroxine but serum t4 actually reduced?

[clairel996]

I was in 25mcg levothyroxine (wokhartd) and had review blood test on 14th MarchTSH 3.92 (0.27 - 4.2)

FT3 4.3 (3.1 - 6.8)

FT4 18.6 (12 - 22)

Started 50mcg (accord) on 22nd March

Thyroid bloods 9th May 2023

TSH 1.39 (0.27 - 4.2)

FT3 4.3 (3.1 - 6.8)

FT4 18 (12 - 22)

Is it usual for the blood t4 level to decrease when increasing levothyroxine? I expected t4 to increase if tsh had dropped?

Approved to start 75mcg (accord) on 12th May 2023 so really don't know what to expect with next bloods in 6 weeks!

[SlowDragon Administrator]

Hardly surprising

Levothyroxine doesn’t top up failing thyroid, it replaces it

As TSH reduces your own thyroid stops working so hard

50mcg is only the standard STARTER dose

Typically dose levothyroxine is increased slowly upwards in 25mcg steps (retesting 6-8 weeks after each increase) until on full replacement dose

Typically that’s approximately 1.6mcg levothyroxine per kilo of your weight per day

Unless very petite likely to eventually be on at least 100mcg daily

[clairel996 in reply to SlowDragon]

Thank you, I'm definitely not petite, around 70kg so probably another couple of increases before I find that sweet spot. Hopefully doctor will be obliging if tsh continues to go down though!

[SlowDragon Administrator in reply to clairel996]

That’s the common issue

GP should NOT dose by TSH

ALWAYS test thyroid levels early morning, last dose levothyroxine 24 hours before test and just water to drink between waking up and blood test ….gives highest TSH and lowest Ft4

[tattybogle]

Don't worry about the T4 not going up yet ,

When you add levo (T4), you are not really 'adding' to the T4 your thyroid can make ,, you are replacing it .

(when you add some ~ initially you have more ... after a few weeks the TSH goes down ... which means your thyroid is being asked to make less T4 , so you end up with the same amount of T4 as you had.

Then your dose in increased,, etc etc . until eventually the amount added is more than the thyroid could make by itself.

So the T4 level only goes up when you are replacing more T4 than your thyroid can make by itself .

Hope that helps.

[clairel996 in reply to tattybogle]

That really helps and makes sense! Thank you for explaining. Iv just cut a 50mcg tablet to be ready to take 75 in the morning and it's a bit more crumbly than I imagined so I might be getting 70 rather than 75! Iv read some people alternate doses so maybe I would be better with alternating 100 and 50 to average 75. Will see how I go with the cutting, doctor was very supportive of me staying on same brand so I can't complain!

[Espeegee]

I'm impressed that you appear to be working with someone who knows how to treat your thyroid problem properly!