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Time of day matters when testing?

Has anyone heard that the time of day matters for testing TSH?  
5 Responses
Avatar universal
Yes..the tsh fluctuates throughout the day at any given time.
That is why they suggest you get labs done first thing in the morning and no meds before the blood test as it will give a false reading if you have taken thyroid meds.
Consistancy is the key.

Usually go on the same day, same time.
if you follow these rules, you will get an accurate lab report.
Hope that helps.
Avatar universal
Thank you it does help.  Except the dr used it as an excuse of why my TSH was up to 3.1 and said that it doesn't mean anything because the past test were normal and this last one was done early in the morning at 8am. "So really I'm normal".  Gotta laugh
744596 tn?1246845015
I did not know any of this. This is very interesting to me. So I should not take my medication before I go to get lab work done? In my mind I always thought I should take it so my numbers wont be too low.

I find this interesting that my doctor(s) never mentioned any of this to me. I just recently was old enough to leave Children's Hospital and move on to an adult endocrinologist and amazed that none of my doctors have ever mentioned this.

Thanks for the information.
Avatar universal
the motto of Doctors here in Australia is NEVER take thyroxin before going for labs as it gives a false reading.
I always 'go naked' so to speak lol.
I am always at the Lab door by 8am and then I take my thyroxin while I am there after blood has been drawn.
Do this each time you go for labs
For example...your FT3 and FT4 may be low,then you swallow thyroxin and the labs show up that they are higher than they really are by taking meds.
Consistancy is the key as I said earlier.
Always go on the same day of the week if possible and always go naked (well you know what I mean lol ....hehehehe)
Avatar universal
TSH is actually highest around 9 pm and lowest around 9 am, and can change by as much as 70%, I've read.  So, if you want the highest TSH reading for test purposes, then go for testing in the afternoon.  As Deb said, just be consistent about the time for testing.

Far better than depending on TSH, which is a pituitary hormone that does not correlate very well at all with hypo symptoms,  get the doctor to test for the biologically active thyroid hormones,  free T3 and free T4.  Free T3 is the most important, since it is four times as potent as free T4 and correlates best with hypo symptoms.
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