Is there a specific reason why we test thyroid levels fasted and before any medication?
My blood test results were queried, as my T3 levels looked high. However I know that the blood test was taken mid-morning, so probably at the absolute peak of my T3 throughout the day. (I wasn't expecting a blood test, otherwise I wouldn't have taken my medication that morning before this).
It then brought up the question of why do I normally fast and not take medication before my early morning blood tests. (Is it so that we have a base level to measure levels of medication against?)
Thanks in advance x
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setay_k
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It depends on what outcome you want from the interaction with the doctors.I do not fast and I don't have early morning blood tests. I have my blood test at 2pm each time give or take 10 mins.
This is because my TSH is supressed so TSH levels are not going to be a problem for me. If you wish to have the highest possible TSH then early morning and fasting.
However I do take my last dose of levothyroxine 24 hours prior to testing and my last dose of lio 8 hours before. This is because I want to measure the trough - the lowest level of hormones circulating. This is because the peak is very short lived and how we peak varies between individuals. It is also more difficult to time consistently on the peak for comparison between blood tests.
Many doctors don't understand about testing procedures.
Thank you Lalatoot, that makes sense. I want to test the trough not the peak. My results are getting scrutinised as I am 6 months pregnant. The specialist at the hospital where I am going for my maternity appts couldn't understand why my T3 was so much higher this time. I had to explain that normally I get a test as early as possible, before I take my meds. Whereas this time I would have taken my meds about 3-4 hours before the blood test.
The endo team I see (useless bunch) stipulate that bloodtest should be 2 - 4 hours after the dose of lio. I ignore this as it would mean that they would keep me undermedicated on a lower dose.
If you don't want to get "bounced" into an unexpected blood test (ie too soon after you've taken your meds) it can be worth a little white lie and saying you've taken supplements with biotin in, which distort the result, so need to book a different date for the blood draw ...
Is there a specific reason why we test thyroid levels fasted and before any medication?
* 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 certain foods can lower TSH and coffee (and possibly other caffeine containing drinks) can affect TSH.
* If taking thyroid hormone replacement, last dose of Levo should be 24 hours before blood draw, if taking NDT or T3 then last dose should be 8-12 hours before blood draw. Adjust timing the day before if necessary.
This avoids measuring hormone levels at their peak after ingestion of hormone replacement. Taking your dose too close to the blood draw will give false high results, leaving any longer gap will give false low results.
* 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.
Thank you SeasideSusie . In your opinion, if you feel well and not over-medicated, would you worry about having an above-range T3? I still have normal/low blood pressure and no symptoms of being over-medicated. When I tested a couple of months ago following all of your advice above I was 'within range'. Upon testing after taking T3 that morning, I was 'above range' at that time of testing.
In your opinion, if you feel well and not over-medicated, would you worry about having an above-range T3?
I would want my FT3 in range if I had taken my last dose 8-12 hours before the test.
If your FT3 is within range when last dose was taken 8-12 hours before test that's fine. If FT3 was over range but you'd taken your T3 before the test then I wouldn't worry about it, it will be measuring the dose of T3 recently taken and showing a false high.
Thanks SeasideSusie , I think I'll do my own Medichecks test at home just for peace of mind and follow the above steps. (The consultant also seems to take forever to send out my NHS blood test results, so I don't feel like I'm fore-armed in conversations).
My only issue is that as I am 6 months pregnant, I am currently taking pregnancy multivitamins (Seven Seas Pregnancy vits), which do contain Biotin ...
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