Hi, I have an underactive thryoid and my next blood test is at 12:10 in the afternoon. Should I fast and not take my levothyroxine beforehand? I asked them if it shouldn't be done in the morning and they said no, it makes no difference.
Many thanks for any help
If you’re hoping for dose increase in levothyroxine, you will be better need to test early morning
Cancel and Rebook test (saying work commitments etc) mean you need early morning test
What vitamin supplements are you currently taking
Remember to stop taking any supplements that contain biotin a week before all blood tests
TSH has pronounced daily variation
healthunlocked.com/thyroidu...
So it’s important when you test TSH ....
researchgate.net/publicatio...
“According to the current TSH reference interval, hypothyroidism was not diagnosed in about 50% of the cases in the afternoon.”
“Further analysis demonstrated inadequate compensation of hypothyroidism, which was defined in 45.5% of the morning samples and in 9% of the afternoon samples”
If delaying taking levothyroxine until after blood test, you likely want to not eat or drink anything apart from water before taking levothyroxine
It may (or may not) make a difference to TSH if fasting ….opinions differ
ncbi.nlm.nih.gov/labs/pmc/a...
ncbi.nlm.nih.gov/pubmed/252...
Thank you so much for your reply
I had my test with the GP practice at 1.45pm after taking my levo. It showed everything was fine but a I didn't feel fine . After seeking advice from this amazing group I took a private test before 9am without levo and no vitamin supplements for 5 days prior. The results were very different showing I was undermedicated. The TSH which they pay most attention to 0.63 on GP test but 1.98 on private test. I shared my private test results with my GP. She was astonished at the difference and couldn't account for it. I explained I had been reading up and learned this was the optimal way for tests to be done. She increased my levo and ordered further bloods for the end of June to be taken under the same conditions as my private test.
In your shoes I would contact the practice and rearrange your test time and follow the advice from SlowDragon.
Hi, you should have your bloods taken first thing, and be fasted.
Hi isisis,I too have underactive thyroid ( 2 years in) and have always had my test done after food and taking my Levo..I take my Levo early morning and wait at least 1/2hr before food..hope that helps.
Take armour before blood test ? 
Levo and afternoon blood test
When to take levothyroxine and taking before blood test
Meds before blood test
Should I take medication before thyroid blood test?
