How long before a blood test

[Pinkpeony]

I was called into the doc's the other day for a blood test . I have had so many lately and didn't know it was for thyroid . I had taken my ntd a short while before the appointment .

I was thinking the results would be ' over the top ' but quite the reverse . The readings are barely in the parameters .

How long is too long before a thyroid blood test ? TIA Pp

[SeasideSusie Remembering]

Last dose of NDT should be 8-12 hours before blood draw.

TSH and FT4 tend to be low when on NDT, it's the FT3 result that's the important one.

[Pinkpeony in reply to SeasideSusie]

The t3 is just inside the parameters . It would have been barely an hour since I took my meds . Thanks SS

[SeasideSusie Remembering in reply to Pinkpeony]

Sounds like you could be undermedicated then. Do you think you are?

[Pinkpeony in reply to SeasideSusie]

To be honest Susie I have had such a bad year I don't know what's wrong with me . I am waiting on the results of so many blood tests . They always try to pin it on the thyroid and the ndt but a thyroid function test ordered by the respiratory consultant in August was perfect .

I just wondered if the fact that I had just taken my meds had altered the reading .Pp

[SeasideSusie Remembering in reply to Pinkpeony]

I just wondered if the fact that I had just taken my meds had altered the reading

What it could do is give you a false high FT3. When you take your thyroid meds too close to the blood draw, it measures the dose we've just taken. However, it depends how long before the blood draw. If less than an hour, it's possible that it hadn't been absorbed properly and not yet entered the blood so then it would depend when you took your previous dose.

[Pinkpeony in reply to SeasideSusie]

Approx 23 hours as I take it only once a day . Pp

[SeasideSusie Remembering in reply to Pinkpeony]

OK, so if the NDT you took before your blood test was less than an hour before, and hadn't been absorbed, then you have a false low FT3 based on your previous dose being 23 hours before. It really would be better to try and get a test done under the right circumstances to give an accurate result because we now can't know if you're undermedicated or not.

But if you feel OK, they may be no need to do anything

[Pinkpeony in reply to SeasideSusie]

Thanks Susie . Will see how it goes Pp