Timing from taking last dose of levo. to doing blood test.

[lucylocks]

Hi

I have been looking over my last years results.

November last year I was taking 132mcg levo.

I only left approx. 17 hours from my last dose of levo. to blood test.

Results.

TSH 0.018 range 0.27 - 4.2

FT3 5.28 range 3.1 - 6.8

FT4 18.1 range 12 - 22

March this year, I was taking the same dose and I made sure I left 24 hours from dose to blood test.

Results.

TSH 0.011

FT3 5.07

FT4 23 all same ranges.

Can someone please let me know let me know if in the November test the FT4 is lower because I only left 17 hours.

Someone else said they thought it would have been higher because of the shorter time period.

Thank you.

[jimh111]

You only need to leave about four hours or more. The longer the gap the lower your fT4 provided your thyroid is not active. Your hormone levels are quite high and this will increase the rate at which you eliminate thyroid hormone. Perhaps this is why your fT4 was lower in the first test (when your fT3 was higher).

[lucylocks in reply to jimh111]

Thank you, but not sure I understand, as the longer gap made my FT4 higher as in the March result.

Also as you say my levels are quite high, could this be causing the panic feelings I am getting?

Also it is always advised on here to leave 24 hours between last dose and test.

[jimh111 in reply to lucylocks]

On average a longer gap will allow more time for levels to fall. It’s quite possible your have a little thyroid function left and this could have influenced the result. In heathy people thyroid hormone levels move around, this is normal. It could be that you cleared out your thyroid hormone a little quicker the first time, just a normal day to day variation. I wouldn’t worry about it, thyroid hormone levels vary, even if you are reliant on tablets. It’s the general trend that matters.

High hormone levels do cause anxiety. If your panic feelings go away when you reduce your dose you know it is from too much hormone.

The 24 hour advice is to get a result that gives a higher TSH. Waiting 24 hours will give an fT4 figure that is about 5% lower with little effect on TSH. As long as you leave 4 hours plus there’s no problem.

[lucylocks in reply to jimh111]

Thank you,

so because I have left quite a long gap on both tests, would my FT4 be actually higher than the results say, and if it is, then could it be well over range especially on the March test.

I was taking 132mcg. levo. on both tests and have now reduced to 125mcg. panic feeling is slightly better, wonder if I should reduce further.

[jimh111 in reply to lucylocks]

Maybe a few percent higher, a negligible amount.

[SeasideSusie Remembering]

What time did you take each test?

[lucylocks in reply to SeasideSusie]

Hi

both around 9.00am maybe the March one may have been 10 mins. earlier.