Thyroid blood test: I have read that there's... - Thyroid UK

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Thyroid blood test

jo_c_2001 profile image

I have read that there's certain times best to have the blood test and that I shouldn't take my thyroxin within 24 hours before it (I think). Also about fasting beforehand? I have my yearly check being done next week but it isn't until 3.20. Any advice please? Still have tiredness and brain fog symptoms so trying to wrap my brain around all this :/ Really appreciate any advice :)

5 Replies
shaws profile image

Cancel this appointment and make one for the very earlest, fasting (you can drink water) and allow a gap of 24 hours between your last dose of levo and the test and take afterwards.

This helps keep TSH at its highest as it drops throughout the day and prevents doctor adjusting dose unnecessarily.

My advice is to cancel that appointment and wait until you can have an early morning test. TSH is highest early in the morning, and drops throughout the say, so it will be be pretty low at 3.20. It also drops after eating, so it's best to fast over-night, just drink water. As doctors only tend to look at the TSH, we want it as high as possible.

It's best to leave a 24 hour gap between your last dose of levo and the blood draw. Whilst that won't make any difference to the TSH, it will to your FT4, should your doctor test it. If you take the levo a few hours before the test, it will give you a very high FT4, your doctor will think you're over-medicated, and reduce your dose. :(

Oh wow ok. It's so complicated :0 Thank you so much for your replies. I will cancel this one and re-book it. As far I know I am only having the basic thyroid test which from what I can make out is the tsh one.

If your surgery just doesn't so blood draws in the morning then ask if you can have a request form to take to the hospital lab and get it done there.

I have an appointment for in the morning now :)

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