Levothyroxine and blood test: Just a quick... - Thyroid UK

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Levothyroxine and blood test

Molly139 profile image
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Just a quick question, I’m booked to have bloods took tomorrow morning at 9:30. I’ve had my 75mcg of levothyroxine this morning at 6am. What would you recommend for taking my dose tomorrow I.e if I leave it till after the blood test it will be 27/28 hours which I have read will show a low TSH. Thank you

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Molly139
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fuchsia-pink profile image
fuchsia-pink

Having an early morning blood test gives the lowest possible TSH reading. The gap of more than the 24 hours recommended here will slightly reduce your free T4 and free T3 compared with a 24 hour gap, but my understanding is that TSH is much slower to react to this sort of small timing change

greygoose profile image
greygoose in reply to fuchsia-pink

Actually, early morning gives the highest TSH reading. And, leaving a gap of slightly more than 24 hours between the last dose of levo and the blood draw won't have any effect on the FT3, it will just slightly affect the FT4. But, yes, the TSH is very slow to react, so a difference of hours won't change the TSH. :)

fuchsia-pink profile image
fuchsia-pink in reply to greygoose

Sorry - meant highest obv!

greygoose profile image
greygoose in reply to fuchsia-pink

Not obvious to someone who knows nothing about all this.

Molly139 profile image
Molly139 in reply to greygoose

Thank you x

greygoose profile image
greygoose in reply to Molly139

You're welcome. :)

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