Question about accuracy of free t4 test

[shirlzoni]

Hello, I had a recent blood draw in which my GP threw in a T4F without telling me so I took my thyroid medication like usual and had the blood drawn about 3.5 hours later. I usually skip my meds until after a blood draw if I’m expecting thyroid labs to be done.

My T4 level was 1.9 (0.8-1.7) and I’m wondering if anyone can here might know by how much my level is falsely elevated from taking the medication beforehand? I’m anticipating that my GP will tell me I need to lower my dose but I feel better since raising it 6 weeks ago from 75 mcg to 100 mcg so I want to make a case for repeating the lab so I can skip my dose until afterwards amd get an accurate result.

Any help would be most appreciated!

[greygoose]

Impossible to say with any accuracy, because it would be different for everyone, depending on how much they were taking, how well they absorbed, etc.

There was some talk years ago about 20% as a rough ballpark figure, but I haven't heard anyone mention that for some time. But it would only be a guess at best.

Always check what they've ordered before baring your arm. They're sneaky like that, slipping tests in unexpectedly.

[shirlzoni in reply to greygoose]

Thanks for the quick reply greygoose. I checked the upcoming tests online before I went in and it wasn’t there but when I got the results it showed up. That’s happened before with other tests so I should have known to withhold my meds until after the blood draw just in case and will do that from now on. I take Tirosint-SOL and it absorbs the best of any thyroxine I’ve ever used. If I can get a repeat I’ll post the results so others can see the difference.

[greygoose in reply to shirlzoni]

You're welcome. You just can't trust anybody, can you!

[shirlzoni in reply to greygoose]

Got that right!

[tattybogle]

,hi, see the 3rd reply to this post for some references to use on your Gp re. timing of levo before blood tests : healthunlocked.com/thyroidu.... my-list-of-references

[shirlzoni in reply to tattybogle]

Thank you tattybogle!!