Book Test as early as possible Monday or Tuesday morning and post back via tracked postal service
Stop taking any supplements that contain biotin a week before all blood tests
If testing iron/ferritin stop iron supplements week before test
All thyroid tests should be done as early as possible in morning before eating or drinking anything other than water and last dose levothyroxine 24 hours before test
Considering that the 600ml microtainer will do 10 tests with Medichecks - TSH, FT4, FT3, thyroid antibodies, Vit D, B12, Folate, CRP and Ferritin, I imagine that if you managed to get 400ml for just the Vit D test there wont be a problem. They wont refuse it anyway, if the blood is viable they will test, only if the blood is damaged (from squeezing it out) or not enough will they not be able to do it.
I always use the dried bloodspot test that SlowDragon has linked to, so much easier and better, and that too is an NHS lab.
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