DD Hair test

Many of you know about chelation on here. I want to order the Doctors Data Hair Toxology test. Just wondering though, Can I take hair from the bottom? I have had my hair highlighted on top a few months ago..
The bottom layers are untouched. Would be a true analysis?
(I have Cutler's book on the counting rules and plan to use this. I decided I don't want to start pulling metals now, with a crown that I can't remove at this time. )