Levothyroxine and blood test

Why do we have to miss our thyroid medication before our blood test ,I take mine at night so having bloods done in the morning soon so if I miss night before and take after bloods then I will be taken them again at bedtime so it's like double dose in one day ,Why miss if it takes 6 weeks for a change in dose so show up in our bloods as I can't understand that , thanks ,

10 Replies

  • Because  Professor Anthony Weetman acted as expert witness for the GMC (and he was the President of the BTA) at the fitness to practice trial of Dr G Skinner in 2007.  

       At this hearing, on about day 3,  Weetman  conceded that taking medication a few hours before a blood test would skew the results.      The transcripts are available online.

    Xx g

  • The results can be a litle out if you take levothyroxine within an hour or two of taking the blood but taking it the night before is fine, in fact I'd expect it to give the most accurate result.

  • My endo was very clear - told me do not take Levo in 24hours before a blood test.

    I normally take at bedtime - so delay and take it immediately after blood test (and don't eat for an hour after) 

    Fine to take next dose that same evening. 

  • > I normally take at bedtime

    Locally an expert recommends this. Acts often like a small increase of your dose


  • I don't know where these endos get their ideas from, I suspect it is 'old wives tales' (please excuse the sexism and ageism).  About four hours is plenty of time for levothyroxine (T3 medication is much more complicated).  See ncbi.nlm.nih.gov/pubmed/335... , note I haven't had time to read the text, I've just referred to the graphs.

    If you allow 24 hours you need to add about 10% to the fT4 figure to allow for the seven day half-life and also make a much larger allowance for the TSH which will be higher than it really is.  I wonder if the endos realise patients do better on higher doses and are fiddling the blood test in order to justify treatment .

  • If I were you I would drop the evening dose and take medication directly after blood draw.  Do not wait till night and take a double dose.

  • Why take a double dose as that is bound to effect my sleep and how I feel ,surely blood test would be more accurate if I take it slightly earlier the evening before and then bloods will show how I am ,

  • Why would it affect your sleep? Or how you feel? It's T4, the storage hormone. It doesn't do anything quickly. You could take your whole dose once a week, and it wouldn't change anything. The important thing is that at the end of the week, you've had a full dose x 7.

  • I take 75mg one day and 100 mg next day and I always feel better in the morning when I have had 100 night before , also I was told by a private doctor once that it is not good to take all the weeks dose at once as messes up your thyroid ,it's not a natural thing to do .

  • Totally agree that it's not a good thing to do, or natural, and I wasn't suggesting anyone do it. I'm just saying that not taking it one day, and taking double the next, is not the end of the world.

    However, you could always take your Levo in the morning of the day before the test. That way you won't have to take it the night before.

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