forgot to stop taken my biotin and levothyroxine before a blood test

[barb62]

Hi People,

Could you tell be how the thyroid testing is affected by Biotin and levothyroxine. I forgot to stop taking Biotin and I took my Levothyroxine at 4am on the morning of my bloodtest. How is the TSH affected - up or down?

[fibrolinda]

Biotin for me gave me false low TSH and false high ft3 and ft4. My ft3 for example was 6.7 'top range 6.8' when still taking biotin but 4.37 when stopping biotin for 5 days. With the Levo I would assume you would be measuring the dose you took so not accurate way of seeing if dose correct etc. Someone with working brain will hopefully be along to explain properly 😊 And not all labs use biotin in tests so maybe check the one you are having tests done at does... Or doesn't.

[greygoose]

Taking your levo before the test will only affect the FT4, not the TSH. Biotin may or may not affect the TSH. Impossible to tell. It depends whether the lab uses biotin in the testing, as fibrolinda said.

[barb62 in reply to greygoose]

Hi Greygoose, my T4 has been at the top of the range for the last three tests (19) it will be interesting to see if it alters. TSH rock bottom last time 0.20, but feel better for it. incidentially, I have Hashimotos and on 100 levo

[greygoose in reply to barb62]

If you took your levo at 4 am, and the test was in the morning, your FT4 will now be well over-range. You need to leave 24 hours between your last dose and the blood draw, or all you are testing is the last dose you just took.

[SlowDragon Administrator]

Most important to test FT3, vitamin D, folate, B12 and ferritin too

Can use Biotin as Good excuse to get a repeat test if these are not included

I often use the biotin reason to avoid unexpected or afternoon blood tests

Never take Levothyroxine in the 24 hours before blood test

[Angel_of_the_North]

Taking your levo will give a false high Free T4. What biotin does depends on the type of assay used by the lab. Readings could be too high or too low. Most often, TSH is shown as low when it isn't, and free T4 and free t3 as higher than they really are. If the lab uses a type of assay not affected by biotin it will make no difference. Don't expect GP to know.