timing blood test when taking levo @ bedtime

[themomx6]

hello everyone, i have to do my labs and i know i have to do it 24 hours after the levothyroxine dose----but i take my pill @ bedtime. so how does everyone time the lab test for that? thank you

[Jaydee1507 Administrator]

Full information is given in this pinned post. healthunlocked.com/thyroidu...

Remember to stop any biotin containing supplements 4 days before the blood draw.

[jimh111]

There is a small spike in fT4 reading a few hours after taking levothyroxine but taking it the night before will have no noticeable effect on fT4 or TSH.

[SlowDragon Administrator in reply to jimh111]

jimh111

That may be true for you….but it isn’t the case for many members

[jimh111 in reply to SlowDragon]

There is a small spike for a few hours after ingestion. Assuming a seven day half life total T4 will decline to 96% after 10 hours and 91% after 24 hours. This is a trivial effect close to the accuracy of a T4 assay.

[Brightness14 in reply to jimh111]

You are in the dog house, I am in it too often as well.

[SlowDragon Administrator in reply to jimh111]

That’s not the experience of many members. We see much bigger difference than that if test at 12 hours after dose compared to 24 hours after dose

[jimh111 in reply to SlowDragon]

Limited studies suggest the difference is small. However, we should consider the effects of fiddling the results for people on levothyroxine.

It's important to have accurate results reflecting average hormone levels, for research and education. If doctors were to consistently see higher TSH associated with symptoms it will only reinforce their faith in TSH assays.

The other issue is most cases of persistent symptoms we see on the forum is from people with a TSH that goes low with average hormone levels. The problem is not a failing thyroid gland (may be that also) but a pituitary that is secreting insufficient TSH with reduced bioactivity. If doctors don't see low TSH with profound symptoms they will never consider anything other than primary hypothyroidism. We see this in the latest BTA / BTF recommendations that sabotage all the work we have done in getting T3 prescribed.

If doctors see a normal TSH when real fT4 is above average (because we've fiddled the blood test) they will quite reasonably prescribe more levothyroxine. Not only is this the wrong medication (T3 is needed) but it endangers the patient. We now know that above average fT4 levels are associated with cancer and cardiac harm. Above average fT4 levels proliferate cancer. We should not inadvertenly promote harmful therapeutic options.

[SlowDragon Administrator]

If you normally take levothyroxine at bedtime/in night ...adjust timings as follows prior to blood test

If testing Monday morning, delay Saturday evening dose levothyroxine until Sunday morning. Delay Sunday evening dose levothyroxine until after blood test on Monday morning. Take Monday evening dose levothyroxine as per normal

Remember to stop taking any supplements that contain biotin 5-7 days before any blood test as biotin can falsely affect test results

[tattybogle]

personally i go for the simple option ... i just bring my bedtime dose forward a little to eg 9 pm to give 12 hrs until 9am test .

12 hrs is long enough to avoid the worst of the peak .... by 12 hrs the fT4 level should be pretty much back down to the base level ~ yes it will drop a bit further during the following 12 hrs , but the differences in level during that 2nd 12 hrs are nowhere near as large/ unstable as they are during the first 12 hrs .

No method is perfect .

The other method (delaying sat evening dose until sunday am , etc....) means that at the time of testing , you have one full days dose missing (which you put back immediately after the test) ..... so that method gives you a slightly 'low' result ,whereas the simpler method gives you a slightly 'high ' result .

it's a question of picking which you want and understanding why you are doing it ,

in an ideal world we'd get 'peak' (4hr) measurements so we knew the top end and could make up our own mind about any risks of having higher fT4 for a proportion of the day , AND baseline (24 hr) measurements so we knew the bottom end , and then we could make more informed choices.

But with the limitations / attitudes of the NHS .. if we want to know our 'peak' levels it's usually better to test that privately 'for your eyes only'