So this is the second time my gp has done this - they've sent me away with a non-fasting form for my first retest of ft4 and tsh - I turn up at the bloods clinic, having fasted, telling them the form is wrong and they're pulling a face at me, obviously thinking "why does this guy think he knows better than a doctor", but then evidently I do cause the first time I was getting actually tested for hypothyroidism along with a lot of other things they did the exact same thing, only I caught it straight away last time and got it changed before the test - as it is now, I've had to walk away and wait another week.
Everything I've seen about bloods on here and elsewhere say they should be taken as fasting, but now I'm second guessing myself as the first time I was also being tested for diabetes with a fasting glucose.
So just for clarification before I find a new gp; these tests should ALWAYS be fasting, yes?
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Warriorduck
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The theory is - and I have seen differences in people's blood work on here - that the TSH drops after eating. Maybe it depends what you eat. Maybe it's difference from person to person. I doubt very much research has gone into the subject. But, best to be on the safe side and always fast.
TSH drops a llittle after food. This might be due to an increase in somatostatin after food as somatostatin suppresses TSH a little. I haven't studied the research in detail but I suspect some research measures TSH before and after food, this is no use as TSH falls during the day.
Some people have blood taken early in the day whilst fasting. This is to get the highest TSH figure they can get a diagnosis or increase in meds. Fair enough if the doctor is a TSH nut. The problem with an early morning blood draw is that TSH is declining, on a downward slope and it will be difficult to compare one set of results with another, you don't know where on that slope you were. Fasting will raise your TSH a little and so may help get a diagnosis. Personally I'd rather be well fed and able to take on a problematic doctor.
So fasting isn't necessary unless you have a difficult doctor. If you're worried just leave two or three hours after eating before having the blood taken. I usually have my breakfast and mid-morning toast and then have the blood taken around midday, after which I go for a coffee and pain au chocolat as a reward.
My surgery does their own blood draw for testing so I don't know about how it works at your clinic. But why do you tell them you have fasted? Why tell them the form is wrong?
It's just never discussed at my surgery. I make an early appointment, I fast, I take my thyroid meds after blood draw, there is no discussion, nurse doesn't ask, I have no reason to tell them.
Thanks for the replies guys, seems I was a bit hasty :'D
To be fair, I've had many problems with my current clinic, some of the staff are unhelpful and rude, and some of the doctors aren't much better, so I tend to get a bit...short when I go there now :') especially after the last time when the form said "fasting glucose" yet didn't have the fasting box checked, resulting in them trying to tell me it wasn't a fasting test and having to faff about for 10 minutes to get them to check with the doctor and get it changed
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Does TSH blood test have to be a 'fasting' blood test please? 
Updated results TSH, fT3 & fT4, ferritin and folate
Optimal fasting and draw times for thyroid blood tests 
suppressed TSH and high FT4
