Don't know about the toxic metals test, but read in the Daily Telegraph Jan 17th P22 that
hair mineral analysis is unreliable for detecting mineral dificiencies. They sent sample hair to the 6 main labs in the USA, and found up to a 10-fold difference between the highest and lowest levels for 12 of the 31 minerals tested. Didn't test British labs though. They concluded testing was only as good as the lab involved.