Combination pill t4+t3 before blood test

[ilenuca]

if I am using Novothyral in the morning which is a combination pill t4+t3 when should I take the last dose before the blood tests?

[Lalatoot]

12 hours

[SeasideSusie Remembering]

ilenuca

8-12 hours. When T3 is involved, in whatever form - NDT, combination synthetic T4 and T3, or Levo plus T3 or T3 alone, it's the T3 that dictates the time gap because of it's short half life. Adjust time of dose the day before if necessary.

[Gingernut44 in reply to SeasideSusie]

Pardon me for gate crashing this post but something I’ve been pondering, if, when on NDT, you take your last dose 8 - 12 hours before your blood test, does that not give you a false high(er) FT4 ?

[SeasideSusie Remembering in reply to Gingernut44]

Gingernut44

It's a choice between a false high FT4 or a false low FT3. When taking any thyroid hormone replacement containing T3, the T3 tends to lower FT4 anyway so that's unlikely to show high. It's the FT3 result that is most important result when on combination meds so that's the one that needs to be as accurate as possible. Taking NDT or combination T4/T3 24 hours before test, which is what's recommended when taking just Levo, is going to give a false low FT3 and could lead to over medication if dose was adjusted by that FT3 result.

[Gingernut44 in reply to SeasideSusie]

Thanks for your reply, it was just that, if NHS labs only test TSH and possibly FT4, then it could cause a dose decrease if the FT4 was showing higher than it would be 🤔

[SeasideSusie Remembering in reply to Gingernut44]

Which is why it's a total nonsense when on NDT or combination T4/T3 to not test FT3 and if this is what's being prescribed then the doctor really ought to know how it works and what needs testing. Far too many hypo patients are being kept unwell by ignorant doctors who don't know how to treat hypothyroidism properly.