Best time of day to have FT3 test ?

[Milpol]

Dear All,

Happy New Year!

Please could anyone advise on the above question. I think your T3 level drops mid afternoon, so would this be the best time for testing to get the lowest reading?

Many thanks x

[jimh111]

Assuming you are not taking thyroid hormone fT3 varies by about 6% during the day. Not worth the bother. I assume this would also hold for someone taking levothyroxine only.

[humanbean]

Graphs of the variation in TSH, Free T4 and Free T3 over 24 hours can be found on page 2 of this paper :

reboundhealth.com/cms/image...

[jimh111 in reply to humanbean]

Note the values for the fT3 graph, about 5.2 to 5.6. The graph is a bit misleading at first glance because they have zoomed in, not shown the origin. I have seen a paper which showed the TSH diurnal variation is preserved for patients on levothyroxine. Can't remember the paper but I'd be surprised if anyone was that keen to see it.

[Milpol in reply to jimh111]

Many thanks jimh111.

[Milpol in reply to humanbean]

Many thanks humanbean x

[silverfox7]

I think consistency is important and as I take my basal temperature anyway then that's the one I record. It doesn't appear to make a huge change whenever you take T3. I wastold go take it first thing but check temperature first thing then about 3 pm and work towards 36.9 in the morning and 37.0 in the afternoon and taking NDT I now take it all at once in the morning as often missed the second as I forgot about it! So back to the consistency point again.

[Milpol in reply to silverfox7]

Thanks silverfox7. Information much appreciated x

[Angel_of_the_North]

You really need TSH, free T4 and free T3 done together so you can see if they are "in balance"

[Milpol in reply to Angel_of_the_North]

Many thanks Angel-of-the-North.

So would that be first thing on a morning on an empty stomach or not necessary?... same as for TSH ? Sorry, still learning about all this 🙄

[Angel_of_the_North in reply to Milpol]

I would tend to do it that way so I could compare all my tests.

[Milpol in reply to Angel_of_the_North]

Thank you ☺️