Thyroid UK
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Best time of day to have free t3 blood test please?

Hi my doctor and lab have agreed to test my free t3 levels. I am undiagnosed and not on medication so want the best time to go have them done to show the true levels. I have read afternoon for t3, and early morning for tsh?

i am only having

free t3



advice greatly received as need a fighting chance

3 Replies

Go here:

That blog has a reference to a paper which is expressly about rhythms and how they vary through the day. Go to the actual paper (linked from the blog) and you get graphs which are much bigger.

Time rather depends on what you are trying to demonstrate. Peak? Trough? Somewhere in the middle? And, do remember, the paper is how typical people are - and you might not conform 100% to that norm. So pinch of salt with your reading of it.



I used to have my fT3 and fT4 blood tests in the late afternoon, as unusually my doctor wasn't interested in TSH, and they did show as being lower, as Rod's link suggests. xx


Interesting, i'm due to have my blood drawn at 9am for TSH, FT4, FT3, RT3 and antibodies...I chose this time because specifically because I wanted to know the peak TSH, but I notice that the timing of the test conflicts with knowledge of lowest FT3 levels, which i'm guessing is just as important to know.


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