Thyroid UK

Do you stop your thyroid meds prior blood test or continue as normal

Two thyroid fourms have advised me to stop my meds prior my thyroid bt to show atrue figure.

my doctors said my free t4 16.7 I had not taken thyroxine that morning

3 weeks later I went to oncology in exetrr to have my thyrogloubin done so took my meds as normal. When I went back two weeks later my oncologist was very concerned as my t3 was very high at 28.8 and said to immediately reduce my thyroxine from 175 to 150.

I said I didnt kknow they were being taken I took my meds that morning as thought it was just thyrogloublin. Any way after telling him what I knew he said you must always take your meds before any thyroid meds

What habe you been told please

3 Replies

I doubt that taking your T4 before your test would give such a high T3 unless the dose was too high. As T4 has a relatively long half-life, not taking your dose that morning shouldn't have an impact on your normal levels either however taking it an hour or so before a blood test could cause a transitory higher-than-average t4 reading at the time of the test depending on how long after the dose your blood was taken. Leaving too long (say a couple of days) between your last dose and blood being drawn could give a falsely low reading.

If your t3 test was done several hours after taking your T4 in the morning probably wouldn't have had much of an effect on your T3 level, certainly not enough to raise it that high.

That t3 reading was very high and I'm not surprised your dose has been decreased. I hope the decrease doesn't cause you any problems.

Pink x


Apologies pink nija its the t4 bloods that was too high not t3 should of checked before sending

Gp bts no meds taken since morning day before. I have them done bwtween 9 and 12 noon

The oncologist I would have taken t3 at 5am and 2.30pm and t4 at 9am. Blood test was taken at 4.30 pm

Hope this make sense now


Ah, ok. Easy mistake to make :) I don't think that taking your t4 that morning would have had that much of an effect on an afternoon blood test but I could be wrong. If I'm wrong, I'm sure someone will let us know :)


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