Why is T4 so High?

[Tabitha6]

hi, I'm new here. 13 years ago had thyroidectomy (thyroid cancer). My levothyroxine dose at present 125. T4 result in September was 20, result last week was 23.7. I have to be to be on high dose to keep the tsh low but can't understand why the T4 should be so raised with no change to dosage. Any ideas?

[diogenes Remembering]

Partly imprecision of the test result (+/- 3% or more) and partly time between taking dose and measurement + what you've been eating (can affect T4 uptake in the gut by up to 20%).

[Tabitha6 in reply to diogenes]

Thank you for info.

[Tabitha6]

Thank you for info.

[SlowDragon Administrator]

All thyroid tests should be done as early as possible in morning and fasting and don't take Levo in the 24 hours prior to test, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results

[Tabitha6 in reply to SlowDragon]

Thank you for info.

[Nanaedake]

I've had a partial thyroidectomy. My FT4 is often over-range and I'm not sure why although like you I have a deliberately low TSH.

If you don't have any symptoms I wouldn't worry about it but I do think if they let us add T3 then our TSH would stay reduced but it would lower our FT4 and raise our FT3 which would bring us back into a more normal range and might make a difference to how we feel.