Synthroid Timing before Test

[Andyb1205]

Hi, quick question. Long story short I want to get my blood drawn tomorrow morning as I’m busy next two days. Seeing Endo next Monday.

I take my Synthroid and Liothyronine together at midnight. I’d like to get the thyroid tests done at 8am tomorrow.

I can take the Liothyronine at 8pm today, 2 hours after and 1 hour before food. What I need to know is, if it’s better to leave a 32 hour gap between Synthroid and the test, or to just leave 12 hours for the T4 too.

It’s likely my TSH will still be suppressed either way. Now on 50 T4/40 T3, was suppressed before when on 75 T4/25 T3. What I want is accurate FT4 and FT3 levels.

That in mind, what do you suggest? Thanks!

[SeasideSusie Remembering]

If you leave 32 hours between last dose of synthroid and blood draw you will get a false low FT4.

Advised here, to get a result for normal circulating hormone is to leave 24 hours between last dose of Levo and 8-12 hours between last dose of liothyronine and blood draw, altering time of taking your meds if necessary.

[Andyb1205 in reply to SeasideSusie]

Hi Seaside. I understand the 24 hour rule for Synthroid. But would a compromise work. If a 32 hour gap will give a falsely low FT4, then as a compromise can I simply take it 12hours before. Provided that I’m unconcerned about the TSH but given the long half life, wouldn’t the FT4 still be accurate?

[SeasideSusie Remembering in reply to Andyb1205]

It wont be accurate for normal circulating hormone level as far as I am aware, it may show a higher than normal result for FT4 if you only leave 12 hours. But as you're taking liothyronine then the FT4 result isn't that important, the FT3 is the important one.

[Andyb1205 in reply to SeasideSusie]

For 12 hours I assume you meant it would show a falsely high FT4.

I should add, the FT4 would still be important for me. I’ve noticed that decreased T4 doses increase certain hypo symptoms, despite the T3 being much higher than when I was on T4 monotherapy (T3 would hover around a third of range, always less than 40%).

Last test on 75T4/25T3 T3 was 56% in range, probably even higher now. FT4 was the same as the bottom number where the range starts!

[Singoutloud]

The way I would do it is Saturday night take t3 as usual but wait until 8am Sunday morning to take t4. Then T3 as usual Sunday night. That way the timing for both ft4 & ft3 on Monday morning are correct. You could then either take your t4 straight after the blood test or wait until bedtime to get back into the usual routine