How much does not fasting affect test results

[Pictur]

Was at dr so I asked for my thryoid to be checked. I am taking 100mcg of levrothryoxine 6 days a week. Test was taken without fasting as only slot was available was 12pm. I take my meds before bed, 5 hours after eating. Results tsh 0.07(0.35-5.00), T34.3(3.4-5.9), T419(12-22). My dr wants me to cut back by 2 pills per week. Right now I feel really good and don’t want to mess with things. How much of a difference is there because I didn’t fast to get proper results?

[SlowDragon Administrator]

What an extraordinary regime....100mcg only 6 days of the week

If you feel well refuse to reduce dose

Ft3 is nowhere near top of range

When were vitamin D, folate, ferritin and B12 last tested

[Pictur in reply to SlowDragon]

All vitamins were tested 5 months ago and everything was good. Was not deficient in any vitamins.

[tattybogle]

The biggest difference made to TSH results is because of the time of day , that makes a much bigger difference than fasting /or not.

TSH taken at 8/9 am in the morning would have been higher than TSH taken at 12noon, as it highest in middle of night (ish) and falls towards lowest at around 2 pm (ish)

fT4 will be accurate enough if last dose taken at bedtime, but might have been a little lower if blood taken 24hrs following last dose.

So basically . he's only reduced your dose because of your below range TSH .. fT4 and fT3 are both comfortably within range.

If you'd taken test at 8/9am ,TSH would probably have been a bit higher , no way of knowing how much , but you didn't need much higher to get TSH into range and them he would have probably left you alone.

Not eating breakfast may or may not have any effect on lowering TSH, the one piece of evidence for this is extremely flawed, but we suggest it just to be on the safe side and because it helps to keep test conditions comparable.

If you don't want to reduce, (and i wouldn't if you're feeling better than you have for a while)

you could mention to GP that you know TSH was measured at near its lowest point in the day, and since you feel well you'd really like to stay on same dose 'as a trial ' for another few months...... then when you next do a blood test , do not let them have your arm after 9 am , even if it means you have to wait 5 weeks for an appointment .. i always tell them i can't come at any other time because of work....

GP is more likely to agree to 'a trial' .. they are terrified of overmedicating people and being held responsible.

GP will probably tell you "it doesn't make any difference what time TSH is taken," because they don't teach them that, but when he goes and looks it up he'll discover we are correct.

He'll probably also tell you you will get osteoporosis and atrial fibrilation if he lets you keep you TSH below range.. but that's not true either... i found a very large long term study showing there are no increased risks until TSH is below 0.04, and the 'risks' between 0.04 and 0.4 are exactly the same as for TSH in-range.

And anyway, statistical risk's are all relative.. there's no point avoiding a statistical risk of osteoporosis, by lowering a dose you feel well on to one that leaves you on the sofa instead of walking up hills... since being sedentary has more than a 'risk' of bone loss , it's a definite.

I can find you a link to he study if you want to see the evidence before discussing with GP.

[tattybogle in reply to tattybogle]

p.s when you say "wants me to cut down by 2 pills a week" do you mean 2x 100mcgs ?

6x 100 /7 = 85.7mcg per day

4 x 100/7 = 57mcg per day.. which is almost certainly far too little, the recommended starting dose is only 50mcg...

If he really is adamant that he won't continue to prescribe at current dose, there is no need to reduce by anywhere near that much,

[Pictur in reply to tattybogle]

Yes he wants to reduce by 2x100 and I am already only taking 6x100 right now. That would lower my dose to 4x100 which I know I will not feel well if I do it.

[tattybogle in reply to Pictur]

From my own experience of GP lowering dose by 25mcg , which is effectively what he's asking you to do, caused me to end up constipated and generally go downhill, and i wasn't feeling too good anyway.. we had a 'discussion' after i tried it for 6 weeks and i said " i'm sorry , but i'm going to put it back up myself" after discussing the study below with him ,and telling him about the constipation etc, he put a note on my records say that i understand the risks, and asked me if i wanted to go back to my previous dose of 125mcg.. actually i now take 112.5mcg /day, which is better than 100 was, and because my fT4 was very over range, as well as TSH being lower than he'd like i've left it at that for now, to see how it goes.

In case it's useful here's some links to the evidence i mentioned earlier :-If discussing the 'risks ' of Low TSH with GP you might find the following ammunition helpful :- If you look at the first reply to this: healthunlocked.com/thyroidu... post, (ignore the fact it say's 'more mature')

and click on the links within it , you will find discussions , and a link to evidence that convinced me that it doesn't really present a problem until TSH is below 0.04 and even then , it's all relative.