Found this information from Norwegian thyroid patient association. Oh well who am I kidding, I might be super smart but I do not speak Norwegian. My Norwegian friend found this for me.
As there already is scientific evidence that smoking affects , still in most countries the recommendation seems to be 12 hours. I always get a note from lab to fast and avoid smoking for 12 hours.
Norwegian thyroid patient association recommends 24 to 48 hours. For symptomatic patients who are borderline this can be really important information. Doctors does not seem to know or care that smoking can affect. They might ask if patient smokes but dont know how to use this information when interpreting results.
Of course no one should smoke, bad me... but if I had known that by avoiding smoking for 48 I could possibly get more accurate test results I would have done it.
It also made me think does smoking affect those who are already on medication? Can it affect and make TSH falsely so low that doctor considers patient being over medicated and starts bitching about it when in reality there could be room for higher dosage?