Advice for timing of T3 before upcoming blood test

[Localhero]

Since I last posted, I’ve had 2 adjustments to my thyroid meds. The first in June, when my levothyroxine was increased to 100mcg from 75mcg. The second in August when I was additionally prescribed a trial of 5mcg of liothyronine because my endo reckons I’m not converting my T4 very well, possibly because of a DIO2 polymorphism. I’m due to have a blood test this coming Friday at 9am and, although I feel somewhat better with these tweaks, my hunch is I would benefit from more lio.

Can I ask your advice as to when would be best to take my last dose of lio before this appointment?

My endo said, “take it as normal” - I usually take it around 6 am - “as I’d like to see what it’s doing in your system after 3 to 4 hours.” Also, he said it didn't need to be fasted.

Should I trust this or do something different? So rare to find a medical person whose advice seems to make sense that I find myself doubting...

My most recent blood test results (so, before the lio was added) were:

TSH: 0.92 (0.27-4.2)

FT4: 19.1 (12.0-22.0) - 71% through range

FT3: 3.5 (3.1-6.8) - 11% through range

My diet is strictly gluten and dairy-free. All of my D3, B12 etc markers are optimal.

[SeasideSusie Remembering]

Localhero

My endo said, “take it as normal” - I usually take it around 6 am - “as I’d like to see what it’s doing in your system after 3 to 4 hours.” Also, he said it didn't need to be fasted.

We can tell you what it's doing after 3 to 4 hours. There will be a spike in your hormone level which will show in a higher than normal FT3 result. This will possibly then mean the endo will say it's a good result and wont increase your dose of T3.

To get a measure of the normal circulating amount (and the endo very likely wont agree, some good endos do) then take your last dose of T3 8-12 hours before the blood draw, splitting dose and adjusting time the day before if necessary.

The reason we fast before a thyroid test is because eating can lower TSH. If TSH is not important then we don't have to worry about fasting. If the doctor only uses TSH to adjust dose, then to avoid a reduction in dose or when looking for an increase, we need it as high as possible so fasting is sensible.

[Localhero in reply to SeasideSusie]

Got it. Thanks so much. It was my hunch that that’s what would happen. I’ll stick with the forum’s take on things which, so far, have served me well (for which much thanks!)

[SlowDragon Administrator]

Likely to need more than 5mcg T3 .....more likely 5mcg 2 or 3 times per day

What vitamin supplements are you currently taking

Remember to stop taking any supplements that contain biotin a week before ALL BLOOD TESTS

Recommended on here that all thyroid blood tests should ideally be done as early as possible in morning and before eating or drinking anything other than water .

Last dose of Levothyroxine 24 hours prior to blood test. (taking delayed dose immediately after blood draw).

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip)

If/when also on T3, make sure to take last 2.5mcg of daily dose 8-12 hours prior to test, even if this means adjusting time or splitting of dose day before test

[Localhero in reply to SlowDragon]

I must admit I thought 5mcg was very low...

Ahhh!! Forgot to stop taking my supplements. May try to rearrange my appointment for next week in that case. I’m taking the Igennus super-B complex, selenium, and the BetterYou Vitamin D+K2.

Thanks so much.

[SlowDragon Administrator in reply to Localhero]

When is blood test booked for?

If Monday ....Just stop vitamin B complex now

[Localhero in reply to SlowDragon]

It’s Friday morning this week. So I think it’s best to rearrange, don’t you?

[SlowDragon Administrator in reply to Localhero]

Yes ...too soon

[Localhero in reply to SlowDragon]

Thought so. In the early days of this thyroid lark, I didn’t appreciate quite so much how these blood tests affected things. In reality, one somewhat skewed test can stall things for months and I’m losing my patience for that, I must say!