Have you ever wondered WHEN to get your thyroid lab tests?

[HIFL]

An interesting chart that should be discussed:

tiredthyroid.com/blog/2015/...

[greygoose]

Is she talking about FT3 or TT3?

It would be a bit difficult to test 6 - 8 hours after a dose if you dose at night. And, to be honest, does it really matter? As long as you are consistant in your testing, then surely it's how you feel that counts, not what a lab tech says your levels are.

Also, given that doctors only go by TSH for the most part, if you took your dose in the morning, and had the test 8 hours after, your TSH would be rock-bottom and they'd say you were over-dosed, anyway.

Also, there must be an acculative effect, otherwise, our labs 24 hours after the dose would all give the same reading no matter what dose you were on. Don't you think?

Seems full of pit-falls, to me.

[HIFL in reply to greygoose]

I think the graph would be about the same if it were FT3 or TT3. The point is that T3 falls rapidly and disappears from the bloodstream within 24 hours, and yet most of us test close to 24 hours after a dose!

I have no TSH regardless of when I test, so I have to ignore that part anyway.

[greygoose in reply to HIFL]

Same here! And isn't that the problem with blood tests! They only measure what's in the blood and not what's in the cells. So, you can have high levels in the blood and still be hypo. I'm really not a great fan of blood tests, at all.

I think the reason that we test 24 hours after the dose is more for the TSH than the FT3, given that the TSH is what most doctors look at. (Some of them Don't even know what the FT3 is!) It's called self-preservation. lol

[Clutter]

HIFL, the reason members are advised to take meds after a blood draw is to avoid measuring peaks which often lead a doctor to assume overmedication and subsequently reduce dose.

For people taking T3 only, 12 hours between last dose and blood draw should be ample as the peak will certainly be over and most T3 will be out of the serum. I was advised that if I left 24 hours between last dose and blood draw I could extrapolate the FT3 result by +20% to estimate normal circulating FT3. I've not seen research to substantiate it.

[Jazzw]

The very much missed Dr Lowe used to say that he only used thyroid blood tests at diagnosis, and that after that, they were pretty much useless for telling you how the patient was doing on medication.

I know we talk a lot here about dose tweaks - but the closest answer to "how much thyroid hormone replacement do I need?" is "whatever it takes to make you feel better".

Which is usually more than TSH-obsessed GPs and Endos will prescribe. {sigh}

[Lilian15]

They are talking about levothyroxine when they suggest 24 hours before. It will have no effect on the TSH but could have an effect on the FT4. I understand what they are saying about T3 but how many of us get our T3 tested. Mostly it is the TSH and the FT4. So it is levothyroxine that should be stopped 24 hours before. Professor Anthony Weetman said:-

Quote: The problem with using free T4 measurements if a patient is taking thyroxine is that the level fluctuate after taking thyroxine treatment. Therefore, within the few hours after ingestion there can be a ten or fifteen per cent level difference in level compared to twelve to twenty four hours after ingestion. End Quote.