Do I take my medication before blood test or not?

I'm in a dilemma

I take all my thyroid medication first thing in the morning. I'm on 20mcg T3 and 100mcg T4

Whenever I have a thyroid blood tests done I don't take my medication until after bloods have been drawn (24-26hrs between dose and test)

Tomorrow I'm having blood test in the evening instead of the usual morning blood test. This is to see if there is any difference in TSH and T3 levels later in the day.

My dilemma is:-

Do I take my medication tomorrow morning or not?

If I do then there will only be 12 hrs between meds and bloods

If I don't it will be 35-36 hrs since last meds taken

Not sure how to play this one!!

Thanks in advance

30 Replies

  • W3ndy2159, is this test at the behest of your GP? I ask because TSH levels naturally differ throughout the 24 hr period, so I wondered what, particularly, he was looking to discover eg TSH is at a higher level early in the morning which is why it is generally recommended to have bloods done first thing. Having said that, if it were me (not a recommendation) I would have my last tablets as normal the day before the test ie not on the day of the test, then take them immediately after the test.

  • Thanks hypnoteq for the reply

    Yes this at my gps request to have evening bloods. I also think it would be better to NOT take meds until after bloods.

    The reason for evening test is to see any difference in TSH and FT3 levels.

    I have been having heart irregularities. Not fast palpitations. But slow HB (50-60bpm) with missing beats. An ECG clearly showed up the irregularity. To me it felt like I would have 3 beats then miss a beat,,but the ECG showed I was having 2 beats and a quick extra beat then a long pause.:-/ it's not life threatening but needs sorting out! Hence blood tests and reduction in T4. My GP took an extra medical degree in thyroid/endocrinology in view of becoming an endo so is really clued up on thyroid issues. He's great and really open to In-depth discussion about thyroid issues and T3/NDT/adrenal etc. he is reluctant to reduce my T3 as he clearly sees an improvement in my health since being on combo treatment.

    Latest test on 16th June 2014

    TSH=0.1 (0.55-4.78) = suppressed

    FT3=4.6 (3.50-6.50)

    FT4=15 (9-23)

    Previous test on 13th May 2014




    My Levo was reduced after May tests suggested I am over medicated, and with the heart irregularities. June test show an improvement in TSH and T3 levels however I now have severe hypo symptoms back. :-(

  • W3ndy, I had a prolonged QT interval diagnosed at the same time I was diagnosed with Hashi's 3 years ago. Sounds very similar to what you describe but there's never been any suggestion that anything needs to be done about it and it has never been a factor in my thyroid medication even when I had intolerable palpitations when I was over replaced. My TSH is kept suppressed post thyCa and my current dose is 100mcg T4 plus 40mcg T3.

  • Wow he sounds like a definite keeper then! Sorry to hear about your heart concerns though.

  • Dr Toft in a Pulse Online article says we can have a very low or suppressed TSH if it makes us feel well. If you go to the date July 15, 2006 in the following link, you can see the effect of adjusting meds due only to the TSH can have. Also the first question/answr is informative.

  • W3ndy, T3 will be out of your blood after 6-8 hours so it should be fine to take that. T4 take after the blood test.

    TSH and FT3 follow circadian rhythms being highest in the early hours and lowest at lunchtime through to evening so it is more relevant to have testing the same time each day.

  • Clutter & Wendy: to answer my own question, I wonder if the GP is thinking about this research (see 2nd para) although I don't know if evening bloods are technically nighttime bloods:

    "There is a circadian variation in serum TSH in euthyroid subjects. A similar diurnal variation has been demonstrated in patients with hypothyroidism. In the present study the 24-hour pattern of serum TSH was investigated in eight patients with hypothyroidism of varying severity and in five hypothyroid patients treated with thyroxine (T4). There was a circadian variation in serum TSH in patients with hypothyroidism of moderate degree, and in patients treated for severe hypothyrodism with thyroxine. The pattern was similar to that found in normal subjects, i.e., low TSH levels in the daytime and higher levels at night.

    In severely hypothyroid patients, no diurnal variation in serum TSH was observed.

    A practical consequence is that blood samples for TSH measurements in patients with moderately elevated TSH levels are best taken after 1100 h, when the low day levels are reached."

    Of course,the third para is a bit of a killer, and is a suggestion best ignored ..............

  • I don't understand why anyone could think that TSH measurements are best done after 11am. It can only be to reduce the risk of having to spend money on treating people.

  • Well absolutely humanbean. Thankfully we all know better lol ;-)

  • If my TSH raises later in the day that's good for me. It is suppressed at the moment and I need it to be higher or endo may pull the plug on T3!!! :-(

  • Remember that a suppressed TSH is fine so long as T3 is within range, and yours is :-)

  • Doctors know little about the function of the Thyroid Gland, unfortunately. They have neither learned the clinical symptoms which vary from patient to patient nor how to raise their metabolism. They prescribe medication for 'symptoms' instead of giving an adequate thyroid hormone replacement till the patient is well with no signs of overstimulation.

  • Goodness knows what the GP is thinking hoping to find, or planning, Hypnoteq. Comparing morning TSH with evening TSH is like comparing apples with pears.

  • Well that was why I asked initially Clutter because it would seem only to demonstrate what is already known about the 24 hr cycling of TSH. So to this bear of admittedly little brain, I would have thought that the TSH/FT4/FT3 package was more enlightening because W3ndy's FT3 isn't anywhere near top of range. (Sorry to be talking about you W3ndy, rather than to you :-) ) but I will stand corrected if I'm being particularly dense here, post-glass of wine!

  • Nothing wrong with your little grey cells and analysis, Hypnoteq. Have another glass to celebrate :-D

  • :-) :-)

  • Thanks clutter. I have an afternoon slump. Once I have bloods drawn tomorrow I am going to divide my T3 and take 10mcg at lunchtime instead of 20mcg at 7am along with my T4. I'm wondering if I should start taking my T4 at bedtime again? I change from PM to AM due to having afternoon slump on the suggestion from someone here,(when I started T3 last July.)

  • If this blood test is being done in the evening at your GP's request I would be deeply suspicious about why he wants it done then. I seriously wonder if he is hoping to find a reason to get you off T3 to save money.

  • Yes, that's why I was wondering about an evening test. I think I'd avoid it like the plague m'self

  • My GP is all in favour of me being on T3 as he has seen an improvement in my health. He agrees T3only or NDT may be the right treatment for me. T4 kept me ill for many years.

  • Suzy Cohen pharmacist recommends in her book Diabetes Without Drugs, Chapter 13:

    Doing thyroid test in the morning and eating breakfast. If on empty stomach, it could cause a false elevation in TSH & RT3.

  • I've not read her book Londinium.

    For those of us wanting to avoid a possible reduction in thyroid meds, early morning draws before that day's tablets is definitely the way to go. But I'm not sure though, why without breakfast, the results would be "falsely" elevated rather than just (naturally) elevated. And if diet is critical, whether the converse is also true ie ought we report having eaten thyroid-blocking foods the day before, for instance, so that the results are interpreted accordingly?

    I recently had both a fasting blood test plus a non-fasting thyroid test together, and when I enquired, Blue Horizon said it didn't matter for the thyroid test that I had fasted for the other test.

  • Sorry, I can't answer for Suzy Cohen. I was only providing you with some info that I'd previously noted from her book. I think I noted it correctly. I made a note of it being from Chapter 13, so maybe someone will look it up? I won't be at the bookshop again until maybe this w/e or the next.

  • Thanks Londinium. Sorry, I was musing more than anything, on her use of "falsely" elevated, rather than necessarily expecting you to know what she was thinking - unless she had explained it in her book :-)

  • No probs. Maybe you could sit in some book shop and read the relevant bits?

  • Good idea lol

  • I have to admit I do not take my medication if I am having a blood test that morning. I take it when I get home. I have no idea whether it makes any difference to the result.

  • Joan, it makes an enormous difference if you have a blood test 3/4 hours after having medication as the test will report the high level of medication in your serum rather than your normal serum level.

  • Thanks for your reply, good to know.

  • Thank you for this information. I am having a blood test on Monday and was wondering whether or not to take my levothyroxine before or after. I asked the doctor and she said it shouldn't make any difference but this didn't make sense to me!

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