Quest sends the test out to Biocenter. Its a royal PITA to get it done. I had to get the vial with ascorbic acid in it from Biocenter as Quest couldn't for some reason. I froze the sample then took it into my local quest who had to send it to a lady in the refurral dept who in turn sent it where it should have gone. I had to talk to everyone at every step of the way though to get it done. We did get it though in the end.
http://www.questdiagnostics.com/hcp/testmenu/jsp/showTestMenu.jsp?fn=437.html...
You may have to educate them but yes they can get the test done. I had to prove it to them with the above link. Are you in CA by chance?