Should you take thyroid meds before blood test.

[Jvbhealth]

I've worked in a labs/hospitals/research ctr and all the manuals ive seen recommend that thyroid meds levels should be tested at trough levels. In other words, don't take it till after your blood test.

[LiaDiGee]

Yes, I agree. Everything I have ever read on the subject highly recommends that you withhold taking your thyroid meds until after the blood work has been done.

[jacrjacr]

never take before test and I would say always take test first thing in the morning when tsh is highest and 12 hours after last meds

[Lilian15]

Here is information from Professor Anthony Weetman – Head of Medical Schools (UK)

Quote: The problem with using free T4 measurements if a patient is taking thyroxine is that the level fluctuate after taking thyroxine treatment. Therefore, within the few hours after ingestion there can be a ten or fifteen per cent level difference in level compared to twelve to twenty four hours after ingestion.

[Glynisrose]

True! DON'T take any thyroid meds before a blood test. The endo and GP will only measure whats in your blood not what is working so any thyroid meds will skew the results.

[janine58]

That sounds logical.....and yet my endo, when asked, said it wont make any difference....

[humanbean in reply to janine58]

I'm sorry to say this, but your endo is a twit. With any drug or hormone that goes into the bloodstream, levels of that drug/hormone will alter depending on the time since the last dose was taken.

If dosing of the drug depends on the levels found in the bloodstream then of course it makes a difference to the patient when they last took the drug being measured.

I have often thought doctors get their logic circuits removed at some point after starting university and before graduating.

[SilverAvocado in reply to humanbean]

It's really shocking that they don't know basic things like this.

[humanbean in reply to SilverAvocado]

I agree.

[greygoose]

Leave a gap of 24 hours for T4 and 12 hours for T3.

[Eddie83]

Depends on whether you have to send a "message" to an uncooperative doctor. If your doctor thinks a low TSH means you are going to have a heart attack and all the other legends ignorant doctors believe, then I would avoid taking thyroid hormone for a full 24 hours before blood-draw. On the other hand, if you would like to see what your peak values are, and are going to be looking for results of FT3 and FT4 tests, and your doctor actually understands when you dosed and what the effects of that are, then I would take thyroid about 4 hours before blood-draw.

My doc is not a twit, so I don't worry about when I last dosed.

[helvella Administrator]

On the basis that there is a pronounced peak with a tail after taking thyroid hormone, it is difficult to compensate for that with any degree of accuracy. (You'd only be able to do so if you knew more about the patient - how quickly FT4 and FT3 rise after taking thyroid homones in them as individuals.) Otherwise the person interpreting the results is just sticking their finger in the air to try to take account of the situation.

Therefore, absolutely agreed, ordinary blood tests of thyroid hormones must be done in the trough.

[mistydog]

someone helpfully linked me to this the other day tiredthyroid.com/blog/2015/...