Messed up with Levothyroxine prior to blood test

[jo1001]

I had a blood test on Wednesday 29th January 2020. After the blood test was done I realised that I had completely forgotton to take Tuesday's dose of Levothyroxine. So by the time I had the blood test on Wednesday morning it was about 39 hours since my last dose.

Have I wasted the GP's time having this blood test or will it not make too much difference to the results?

Thank you.

[fuchsia-pink]

Your fT4 result will show a "false low" - so bear that in mind when you get it.

[jo1001 in reply to fuchsia-pink]

These are my results from 29th January 2020:-

Serum TSH 1.05 mu/L Range 0.35 - 5.00 (normal)

Serum free T4 14.4 pmol/L 9.0 - 22.0 (normal)

Serum folate 11.4 ug/L 3.0 - 20.0 (normal)

Serum ferritin 152 ug/L 10 - 200 (normal)

Serum vitamin B12 804 ng/L 200 - 910 (normal)

[SlowDragon Administrator in reply to jo1001]

No vitamin D result?

[jo1001 in reply to SlowDragon]

SlowDragon, no, have checked again on test results, doesn't look like it was tested.

[SlowDragon Administrator in reply to jo1001]

£29 via nhs postal kit

vitamindtest.org.uk

[jo1001 in reply to SlowDragon]

Thanks, will have a look at that.

[jimh111]

Using a half-life calculator after 12 hours (half-way between doses) your fT4 would be about 95% of its peak value. After 39 hours it would be about 85%. So take your fT4 figure and x 85 / 95. Your fT3 would probably be a bit higher than reported and your TSH lower. I wouldn't worry, these are small variances, our levels vary from day to day and for women vary considerably during the menstrual cycle. The numbers are good enough, they are not a precise measurement of thyroid status.

[jo1001 in reply to jimh111]

Thank you.