Diyena It depends what you want to know. If you want to know if you are on the right amount of supplement then continue. If you want a baseline level then leave off the supplements and I think that should be a few weeks, not sure but maybe someone else will know.
I've read that you should leave off iron for a week or so if you've been supplementing, it's important not to overdo the iron.
City Assays, who do the Vit D bloodspot test, say you can stay on the Vit D supplement, just don't take it on the day of the test until after you've done it. They recommend testing twice a year.
I tend to continue the supplements but don't take them on the day I am testing until after the test. If any come back too high, I adjust my dose (just done that with Vit D).
If you want a baseline B12 or ferritin result you'll have to stop taking B12 and iron for 4 months which is the time it takes for red blood cells to die off and renew. If you want to know whether you are taking the right dose supplements just leave off the supplement until after the blood draw.
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