Taking levothyroxine before having blood test

[Ditzy-gal]

Can anyone point me in the direction of evidence or rationale as to why it is best not to take levo before thyroid function test please? I'd like to present it to my gp.

[Treepie]

I am not entirely convinced by the rationale .It makes sense at face value. But taking Levo before and having the blood taken at 12.30 : TSH was 1.9. Increased by 25mcg ,took none for 24 hours and blood at 8.30 and TSH was 1.1.

I was wanting to take more but stymied. I thought that not taking Levo and an earlier blood test would offset the increase I had been taking but not so.

There seem to be many variables but does no harm to follow the accepted line.

[shaws Administrator in reply to Treepie]

The TSH is not static. It varies throughout the day/night. As you took T4 before and test at 12.30 and TSH was 1.9 maybe waiting would have shown a higher TSH and a need for more levo. Next time you waited 24 hours but you had also increased by 25mcg so, by my reckoning, your previous blood test wouldn't have been strictly accurate.

Some take NDT, T4/T3 and T3 only, so the TSH may not be identical in all of these, or the T4, or T3 if this was tested as well. If taking some T3 and having blood test within hours the T3 would show elevated as it peaks within a few hours of digesting and your medication would be reduced, no doubt.

[Treepie in reply to shaws]

You may be right Shaws ,it seems to me that sticking to the advice here is sensible re - the variation during the day and it's not a great hardship to take T4 later.

My GP wants to retest the ferritin ( over 600) along with other tests next time and strongly suggested having at least 3 alcohol free days as he says it will affect T 4 absorption. So he would not increase t4 on grounds I should be fitter on less booze. Just before Xmas! Will be a struggle.

[Glynisrose]

It stands to reason that if you take medication before a blood test that only measures what's in your blood its going to be skewed. Why do you need to prove it to your GP? Just don't take it before a test and don't tell the GP.