I didn't do a hair test for metals; it was enough for me that my body went haywire when I started taking some chelators (DMPS, ALA, chlorella).
From everything I've read online, there is no foolproof way to know if you are metal toxic through lab tests. The metals could be anywhere in your body causing problems, all the way into your bone marrow (lead sinks right into your bones). That's why I am of the school of thought that if your symptoms fit the list, you just need to start chelating and see how it goes.
To be honest, as metal-toxic as our environment is nowadays with lead and mercury in particular, everyone should be chelating periodically anyway IMO.