Taking thyroxine after having blood test not before

[sueoathall]

Recently someone told me how many hours the last dose of thyroxine should be before having blood taken for thyroid tests. I cant find the post now, could someone remind me please?

Thank you

[jimh111]

Don't take levothyroxine within four or five hours of a blood test. If you take it at night there's no problem but if you take it in the morning postpone your tablet until after the blood is taken.

[sueoathall in reply to jimh111]

thank you for replying but I had a feeling it was 20 hours or so?

[SeasideSusie Remembering]

sueoathall

Here is a link to your profile (to find it yourself, just click on your avatar or your user name), and you will find a list of all the posts and replies that you have made:

healthunlocked.com/user/sue...

I have had a look and I cannot find a post where you have asked about when the last dose of thyroxine should be taken before a thyroid blood test; however your last post did ask about biotin but that's all.

Here is the timing recommended on here (Jim has a different idea from the Admins and most other responders here and some endos)

* Blood draw no later than 9am. This is because TSH is highest early morning and lowers throughout the day. If looking for a diagnosis of hypothyroidism, an increase in dose of Levo or to avoid a reduction then we need the highest possible TSH

* Nothing to eat or drink except water before the blood draw. This is because eating can lower TSH and coffee can affect TSH.

* Last dose of Levo 24 hours before the test, take that day's dose after the blood draw. This is because if you take your Levo before the blood draw the test will measure the dose just taken and show a false high. If you leave longer than 24 hours the result will show a false low. Alter timing of dose the day before the test if necessary.

* If you take Biotin or a B Complex containing Biotin (B7), leave this off for 7 days before any blood test. This is because if Biotin is used in the testing procedure it can give false results (most labs use biotin).

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

[sueoathall in reply to SeasideSusie]

thanks very much

[jimh111 in reply to SeasideSusie]

Taking the blood 24 hours after the last dose as opposed to e.g. 10 hours after will give an fT4 result that is about 5% lower. The difference is less than the inaccuracy of the assay and it's not worth messing up you therapy. So, if you take levo in the morning wait until after the blood draw (which will be 24+ hours) but if you take it in the evening continue as normal (and have a gap around 10 hours rather than 34 hours).

[cmt1121 in reply to SeasideSusie]

I was told by 2 endos that 3 days for Biotin

[SlowDragon Administrator]

NHS England Liothyronine guidelines July 2019 clearly state on page 13 that TSH should be between 0.4-1.5 when treated with just Levothyroxine Note that it says test should be in morning BEFORE taking Levo thyroxine

Also to test vitamin D, folate, B12 and ferritin

sps.nhs.uk/wp-content/uploa...