Blood test - fasting required?

[RebsterRoo]

I have a blood test arranged for 10am tomorrow - I suspect hypothyroidism. Is it worthwhile fasting before the appointment or does it not make a difference? GP hasn't advised anything but I want to make sure my results are as accurate as possible

[NatChap]

Yes, nothing but water prior to your test x

[SeasideSusie Remembering]

RebsterRoo

According to member Diogenes (Dr John Midgeley, thyroid researcher and advisor to ThyroidUK) TSH falls after eating:

healthunlocked.com/thyroidu...

TSH falls after eating, but FT4 not affected. Don't know about FT3 but suspect it will behave like FT4.

You need TSH to be as high as possible for a diagnosis of hypothyroidism so a fasting test is advised.

Also, you might be wise to change your appointment. Your TSH will be lower at 10am than at 9am. I would re-book for a day when you can get a 9am appointment. See first graph here:

healthunlocked.com/thyroidu...

These are patient to patient tips which we don't discuss with doctors or phlebotomists.

[RebsterRoo in reply to SeasideSusie]

Thanks for the tips. I will certainly fast prior to the test. As for the time, unfortunately it's difficult enough getting an appointment full stop, so I can't really afford to be choosy about the time. I will go with it and see what comes back. If results are not indicative of an issue I will consider private tests which I can do first thing I think

[MaisieGray in reply to RebsterRoo]

I agree with jimh111. In your initial post you mention that you want your results to be "as accurate as possible", but whatever the circumstances of having the blood draw, the results will be an accurate reflection of that (excepting if you supplement with biotin, and the lab uses biotin in its assay methods, in which case it may skew the results in either direction). As you haven't yet had blood tests carried out, you don't know if your symptoms are a result of thyroid dysfunction or not; and therefore there can be no "right" or wrong result, only the result you get. Manipulating blood test results is a game too many of us end up playing for years - often for the right or important reasons, but nevertheless some people tie themselves up in knots to alter the results one way or another. As you have those symptoms with the life you are living, it would seem logical to test in the same circumstances as the symptoms arise. The aim shouldn't be to skew the initial test results to push a diagnosis, but to find out what is going on now, with the life you normally lead.

[jimh111]

My view is that it doesn't make a noticable difference. The only evidence I've ever seen was during Ramadan fasting where a large meal is eaten in the early hours accompanied by no water, no food during daylight hours. So it you want to postpone your blood test for a month ...

Seriously, a large fatty meal might make a difference but I wouldn't starve yourself, the well conducted studies have found no difference. Many patients disagree with my view.

The intention of fasting is to get a higher TSH result, so it depends on what you want when you say 'make sure my results are as accurate as possible'. Bear in mind thyroid hormone levels fluctuate in healthy people, especially TSH which can vary quite a lot during the menstrual cycle. It's more important to pay attention to signs and symptoms and not get bogged down by the numbers. An elevated TSH and low fT4 would clearly point to a failing thyroid gland but normal results do not exclude hypothyroidism. In the end it is your symptoms and response to thyroid hormone treatment that is the ultimate test.

[RebsterRoo in reply to jimh111]

Thanks jimh. I fully understand what you're saying. Alas I am not currently diagnosed (this will be first blood test) but am having severe symptoms that are massively impacting on my day to day life. So what I really want right now is a chance to access treatment, which I'm only likely to get by getting the 'right' blood test result

[jimh111 in reply to RebsterRoo]

OK. If it applies to you the highest TSH will be attained mid-cycle ncbi.nlm.nih.gov/pmc/articl... , although many patients are hypothyroid because their TSH is too low to stimulate sufficient hormone, particularly T3. Just see what your results are and take it from there.