Tests and B vits

[Caradoc1a]

I have thyroid tests soon and recall advice re stopping B vits a week beforehand. I think I also read to continue with methyl folate instead for that week. Is that correct? I've searched pinned posts but can't see this. I self inject B12 daily at the moment and do not want to stop for a week as I have neuropathy from B12 deficiency. Will this affect thyroid tests? Thank you!!

[helvella Administrator]

Biotin, vitamin B7, is the one that actually interferes with the laboratory testing processes.

So far as I know, the other B vitamins do not interfere in that way. Of course, if you measure B12, then injections will make the result look incredibly high. (But testing B12 levels when injecting is advised against and has absolutely no justification.)

And taking any form of folate (folic acid, methylfolate, folinic acid) would likely show an elevated folate test result simply because of taking it. But, again, I do not know of any actual test interference.

helvella - Biotin supplementation and testing

A short article about how and why biotin can affect blood tests. Includes information about how to avoid any problems and how much biotin some foods contain.

Last updated 03/01/2025.

helvella.blogspot.com/p/hel...

[Caradoc1a in reply to helvella]

Thank you, that very helpful

[Jaydee1507 Administrator]

Its only any supplement containing biotin thats an issue with thyroid blood tests. So mainly biotin only or B complex is affected.

B12 injections are fine as are folate supplements.

Are you also taking vit D as that is a cofactor for B12.

What are your latest test results for folate, D3 & ferritin?

[Caradoc1a in reply to Jaydee1507]

Thanks. I take 4000iu vit D daily. Plus 240mcg vit K2 mk7 each day. Thorne basic b complex daily as well. I'm rattling!! Re latest tests: November 24, Ferritin 123 (28-200)

Folate 9.3 (3-20)

D3 96.6 (don't have the range) done August 24 in orthopeadic hospital prior to zelodranate infusion for osteoporosis.

I'm just about to ask Endo to retest all of these in early Feb when I get Ft3 and Ft4 tested. I've had Levo raised from 25mcg to 38.5mcg from 27/12. I also take 10mcg Liothyronine twice a day. Tests in November were:

Ft3 3.9 (3.1-6.8)

Ft4 7.2 (11-22) labelled as low

TSH 4.53 (0.3- 4.2) labelled as high

Thank you

[Jaydee1507 Administrator in reply to Caradoc1a]

So for you, its just the B complex you need to stop. You can take a separate 400mcg folate instead during that time.

Your folate level is still on the low side so adding another 400mcg folate to your B complex would be a good idea moving forward.

Are you doing thyroid tests as recommended here?

Recommended blood test protocol: Test at 9am (or as close as possible), fasting, last levo dose 24hrs before the blood draw, last T3 dose 8-12 hours before blood draw & no biotin containing supplements for 3-7 days (Biotin can interfere with thyroid blood results as it is used in the testing process).

Testing like this gives consistency in your results and will show stable blood levels of hormone and highest TSH which varies throughout the day. Taking Levo/T3 just prior to blood draw can show a falsely elevated result and your GP/Endo might change your dose incorrectly as a result.

I'm thinking you've left a long time from last T3 dose to test? Your FT3 is probably showing a false low.

Your FT4 is a lot too low and most people need around 100mcg in a combination dose.

Vit D & ferritin are good.

[Caradoc1a in reply to Jaydee1507]

Blood test is booked for 8.30am and will follow all the protocols as advised on here. Last time I left too long a gap between T3 and the test and this time I am more aware of this. When I started Levo I was given 100mcg which ended up with me in A&E with suspected heart attack. So Endo thinks I am intolerant to Levo although I saw on NICE CKS to start with 25-50mcg if over 60 years. I'm 68.

I'm aware that taking B12 injections every day or EOD will use up lots of Vit D, folate and iron so I am also going to ask for an iron panel as well. Excuse to eat dark choccy and lots of dried apricots!!