Originally Posted by mrsD

Here is a post from Consumerlab... that some supplement makers may put "more" vitamin in a product..

I have been having neurological symptoms, and a blood test showed I have toxic levels of vitamin B-6. My multivitamin contains 75 mg of B-6, but this is below the upper limit of 100 mg per day. Could my vitamin contain more than it lists? Answered by

This link explains the steps to do to provide an accurate result. Notice the hemolysis as a condition to reject the sample.
Hemolysis occurs when a butterfly needle is used also.
What it means is that the cells in the blood burst and flood the serum with the B6...giving a false elevation. (this commonly also leads to false potassium elevations also).
Vitamin B6 , Plasma (926)

I am still looking for the actual lab procedures... calibration of the machines,etc...but I am having trouble finding it. When I do I will add to this post.

This link explains how high B6 levels in testing occur in people not taking high B6 supplements.
This seems to be related to the MTHFR mutation:

The Cause of Vitamin B6 Toxicity is Not What You Think


MTHFR genetic errors are being found today in up to 30% or more of people tested.