Levothyroxine and blood test

[Molly139]

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

[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 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 in reply to greygoose]

Sorry - meant highest obv!

[greygoose in reply to fuchsia-pink]

Not obvious to someone who knows nothing about all this.

[Molly139 in reply to greygoose]

Thank you x

[greygoose in reply to Molly139]

You're welcome.