Question

[buzza2007]

Have blood test soon, do i take my thyroxine medication before blood test or after

[shaws Administrator]

After. Test should be the earliest possible and don't eat before it. You can drink water. Leave about 24 hours between you last dose of levo and test and take afterwards.

[Nikki246 in reply to shaws]

I've never had to starve before my blood tests and always taken my medication as normal. Last lot l had done were straight after lunch and it came back my levels were low even though I had taken my thyroxine that morning! Feel much better now my medication has gone up so tests must have come out correctly.

[shaws Administrator in reply to Nikki246]

They may have come out 'correctly but you don't know if they would have been higher. We don't starve ourselves - we just don't have breakfast until after test and you can eat as much as you like the previous day. It's only your thyroid hormone dose that has to have a 'window' between taking the last dose and the test.

However, you are free to do as you think best for you.

Eating before a blood test reduces the TSH that's all.

[debraleee in reply to Nikki246]

You don't say whether you were taking T4 (regular thyroid like Levoxyl) or if you are also taking T3 like liothyronine. Your body can only use the T3 so if your body cannot break down the T4, you can still be hypothyroid. As indicated by others on the Forum, there are many other factors including iron and B12 etc. Be sure you have a doctor doing a wide spectrum of test to get the full picture. Whatever is normal does not need to be retaken but whatever is out of kilter is what needs to be adjusted thru meds and supplements.

[Nikki246]

I have mever been told not eat in the 8 years of being tested and last person to test me was a Professor from Guys Hospital, so I assumed he knew what he was doing! I will ask when I go back. Thanks 😀

[greygoose in reply to Nikki246]

I doubt he will know. This is a very recent discovery and things like that take a long time to trickle up to the giddy heights of professors.

I would never, ever assume that any doctor knew what he was doing as far as thyroid is concerned. After all, if he were so brilliant, you wouldn't need to be here, would you.

[debraleee in reply to Nikki246]

Just because those doctors never told you doesn't mean they were right, because research is ongoing as are treatments and medications. Recent research stipulates not to take any thyroid meds and to take a fasting test. Especially important if your doctor has added a cortisol test to check your adrenals along with your thyroid. I'm 63 and only recently learned so much about thyroid from this forum and by reading valid Medical research. Most General Practitioners only run the TSH test and not the TSH sensitivity or antibodies or free T4 or free T3. Once I saw a brilliant endocrinologist who ran the full spectrum, I was finally able to start recovering though I'm not there yet. Keep in mind any weight shifts you have as that merits increasing or decreasing your dosages as well.

[Singoutloud]

There is a medical research paper that shows the impact of food and afternoon blood testing on thyroid results. Just having difficulties posting the link. Will keep trying but it shows that 75% of patients would have been reclassified as euthroid.

[debraleee in reply to Singoutloud]

What does euthyroid mean? I agree that if you take your meds your blood work is going to reflect the meds in your bloodstream and not your body's metabolism. That just seems to be common sense to me but research also corroborates this

[Singoutloud in reply to debraleee]

I'm rubbish at explaining things but It means that your thyroid looks as though it is functioning normally according to your blood results even if your physical symptoms say otherwise. That's why it so difficult to get a diagnosis or treated with the right amount of medication.

[Singoutloud]

Found it ncbi.nlm.nih.gov/pubmed/252...

[Singoutloud]

This is the full article ncbi.nlm.nih.gov/pmc/articl...

[humanbean in reply to Singoutloud]

I've read that paper before. The methodology that was used was very weak. There is no way to tell, based on the way that the study was done, whether the difference in TSH that was found before and after eating was because of eating or just because the blood samples were taken later in the day when getting the "after eating" sample.

The research paper states :

"Phlebotomy was performed after an 8-12 hour overnight fast between 7:30-8:30 am for free T4 and TSH measurements and the patients returned 2 hours after breakfast for their samples to be rechecked between 10:30-11:00 am on the same day. "

There is clear evidence from other papers that time of test has a pronounced effect on TSH. That may have been all that was necessary to give the results they got on this testing.

If they'd wanted clear proof one way or the other whether eating made a difference they should have designed their experiment differently. It would have taken two days, rather than one.

Day 1 : All participants should get up at 6am but not eat until after blood testing. Take blood samples from all participants at 8.00am, and do thyroid function tests. Then let them eat what they want.

Day 2 : All participants should get up at 6am and eat breakfast as soon as possible. Take blood samples from all participants at 8.00am, and do thyroid function tests.

The only difference between day 1 and day 2 is whether or not people had eaten. Under those circumstances the testing might have proved something. As it is the research proves nothing.

Having said all that I would still fast before getting blood drawn myself. It increases the comparability between different sets of tests.

For example, if I got a blood test done after eating a high carbohydrate breakfast, how would I know whether the results could be compared to tests done after a high protein breakfast? I don't know all the factors that affect the results, and nor does anyone else, including scientists and reserarchers. However, if I have fasted every time then I can make a truer comparison than I could where other variables are chucked in to muddy the waters.

[Singoutloud in reply to humanbean]

Thanks for explaining that human bean. I was going to shove it up the nose of my sons paediatrician who insisted that an afternoon blood test after food wouldn't make any difference but may have to think again. Mind you, I could just wing it and hope she doesn't look at it too closely. Who am I kidding, she'll probably put file under B for bin before I'm out the door. 😊

[humanbean in reply to Singoutloud]

Although I'm not convinced about eating making a change to TSH (it might do, it might not, the research just hasn't been done properly to say one way or the other), I am absolutely convinced that time of day makes a big difference, and early is best if we are looking to get the highest possible TSH.

press.endocrine.org/doi/pdf...

Take a look at the graphs on the second page of the above paper.

[debraleee]

No! If you take thyroid meds within a few hours of your blood draw and lab work then you are reading the meds in your system and not your metabolism. I had to retake all my labs on Friday without taking my medication first. I'm eager to see what the results are.