Disparity with two Blood Tests - Any Thoughts Please As to why T3 so Different

[Delgor]

Hi All, I would welcome any thoughts you may have regarding the following:-

Medichecks test done on 4th May at 8.00 am (fingertip):

TSH: 0.01 (0.27-4.2) FT4: 19.9 (12-22) FT3: 6.1 (3.1-6.8)

Hospital test done on 6th May at 8.00 am (venous)

TSH: 0.01 FT4: 18.4 FT3: 4.9 - Range same as above

As suggested by Seaside Susie no biotin taken, or any other supplements come to that for a week before to make perfectly sure I wasn't messing up in some way. NDT taken 24 hours previously, fasted as usual, only drank water.

[tattybogle]

Even in a person with healthy normal thyroid you could expect fT4 and fT3 to be a little different two days apart.. even half an hour apart you wouldn't get the exact same results, even if you did them at the same hospital without getting out of the chair in between, because T4 and T3 are released in a pulsatile fashion not a steady stream . When you then consider that you have some nodules? playing in the game too , and possibly you walked faster/further to get to one test than the other, and one went by post and took longer to get to a different machine .... then all in all it doesn't really mean much that FT4 and fT3 were a little different on these tests.

But i do understand ,it is annoying when you're trying to figure out what's going on.

But this really doesn't indicate anything is 'going on' , other than that for many of us ,it's impossible to get the same result twice with thyroid hormones. So we have to pay more attention to trends in direction more than individual results.

All labs are also allowed a very small % variation in accuracy of results.

It's only a tiny%..., but when you put all these factors together . hopefully this explains how fT3 can look so different 2 days apart.

[Delgor in reply to tattybogle]

Thanks very much Tattyboogle - there's no doubt I am trying to figure out what it going on and did feel some concern that my T3 had dropped so low which has never ever happened before ever. Cheers!

[greygoose]

You left a gap of 24 hours between your last dose of NDT and the blood draw for both tests? Then both your FT3 results are false lows. You should only leave between 8 and 12 hours, I'm afraid.

[Delgor in reply to greygoose]

Flaming Nora - just when I think I'm getting on top of everyone's advice re: biotin and vitamins etc. another spanner is thrown into the works! I seriously have never been told to do that by any doctor and have been on NDT for 26 years so are you saying that all my previous tests could have been skewed?

[greygoose in reply to Delgor]

If you left gap of 24 hours for each of your previous tests then, yes, they were skewed. However, that's not necessarily a bad thing, given how doctors like to keep people under-medicated!!!

But, no doctor would tell you that, because no doctor knows! They don't think it matters when you take your dose in relation to your blood draw. But, have you not seen that mentioned on here before? We're always telling people to leave a gap of 24 hours for levo, 8-12 for T3, and as NDT has both T4 and T3 in it, it's best to leave the 8-12 hour gap because the FT3 is the most important number. You don't even need to mention it to your doctor, just as long as you know yourself.

[Delgor in reply to greygoose]

As always, thank you so much for all your input - it's very much appreciated! No, I haven't seen a post before regarding this topic before but owing to chronic fatigue and various other health problems I haven't been looking at HU religiously up until recently. I am learning a hell of a lot now that I'm not brain dead on antidepressants and can only thank everyone on here for their very valued support and advice.

[greygoose in reply to Delgor]

You're very welcome.

[Bearo]

I think this shows why NHS guidelines love the TSH test - it’s much more reliable than FT3 and FT4 - so who cares if it doesn’t actually tell you very much?

I had slightly different results from the same blood draw (well, it wasn’t the same, but a private test draw was taken 30 seconds after the NHS draw and popped into a different vial. The ranges were the same but ,of course, different labs then produced the results. Only TSH was the same in the two tests).

[Delgor in reply to Bearo]

Thanks Bearo - I've just clicked onto your profile and found you were also questioning blood results from tests. I'm beginning to wonder what they actually prove and shouldn't endo's/gp's listen to the symptoms their patients actually have. I wish I could take control but with multi nodules coming into the equation I don't feel confident enough to do this - aah!