Blood test tomorrow but overslept!

[MiniMum97]

Hello

Have a thyroid blood test tomorrow at 8.40am but overslept this morning and didn’t take my T4 and first dose of T3 until 10.30.

How bad is this? Should I try to rearrange?

Many thanks.

[helvella Administrator Thyroid UK]

It will have very little effect.

[tattybogle]

No need to re-arrange ..... 'roughly' 24 hrs is 'good enough' ... basically as long as it's over 12 hrs and not longer than about 30 hrs , the difference in fT4 level is so small as to be insignificant anyway.

The main thing we are trying to avoid is testing during the period of about 6 hours after taking the last dose levo ,as there is a very sharp rise and fall of fT4 during that time . ( and fT3 if T3 is taken)

Time of last dose doesn't make any difference to the TSH result .. it's just the fT4 result (and fT3 if taking T3) that are affected by time of last dose .

take your last dose of T3, 8-12 hrs before test.

[tattybogle in reply to tattybogle]

Graphs etc with more detail of what happens to fT4 and fT3 levels after taking the dose in replies to this post : healthunlocked.com/thyroidu...

[MiniMum97]

Fabulous. Thank you both!