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Thyroid UK
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Vitamins affecting blood draw

Hi I read on someone's post that biotin and b vitamins need to be stopped 3-5 days before a blood draw as can affect results. (I'm testing for all thyroid levels and antibodies) Is this right? I have paid for a private blood test tmw and didn't know this... Have been taking vitamins for ages..😏 How does it affect the result does anyone know? Thank you in advance

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If biotin (B7) is in your supplements it can skew the tests which use biotin in their assays. endo.confex.com/endo/2016en...

Who have you bought your blood test from?


Dam it.

Yes vitamins I'm taking do contain biotin.

I'm having a blood draw tomorrow from werlabs uk where nurse comes to the house, although I've also got a kit coming too from medichecks as the original test I bought didn't do antibodies. I was hoping for the nurse to do both tests tmw...

What do you suggest? And how so do they affect results?

So much to learn!


It is not possible to say how your level of biotin would affect your test results. Possibly not at all; possibly significantly.

Unfortunately, susceptibility to biotin interference is variable in magnitude and can skew results to be either falsely high or falsely low depending on the assay design and conditions. The ramifications for patients and caregivers are potentially grave. In typical competitive immunoassays for small molecules such as free thyroxine (fT4), free triiodothyronine (fT3), testosterone, estradiol, and cortisol, biotin interference blocks assay signal. Because signal is inversely proportional to analyte concentration in competitive assays, biotin can cause falsely high results. In the 2-site “sandwich” immunoassay format [typical for larger protein analytes such as thyroid-stimulating hormone (TSH), thyroglobulin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), insulin, and for autoantibodies], excess biotin competes with the biotinylated complex causing a reduction in signal and a falsely lower result. This combination of 2 types of biotin interference can create the perfect factitious biochemical evidence of Graves thyrotoxicosis with highly increased fT4 and fT3, positive TSH receptor antibodies and suppressed TSH. Similar scenarios of biotin interference can be imagined for extremely high steroid hormone concentrations with suppressed LH or FSH, which would be suggestive of tumors.


BUT - how much biotin are you taking? If it is only 30 micrograms, likely has no impact. If 10 mg, then far more likely to have an impact - though only if the tests you are having done are susceptible.


I know that B vitamins and Vit C moderate inflammation and, therefore, must surely affect lab results pertaining to inflammation and cardiovascular conditions.

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