I think I may know what you are asking here.  Did you take your medications as prescribed and then it did not show up in a test to see whether you were taking it?  And then your doctor dismissed you from his care?  Or are you talking about drug screening in which the xanax did not show up yet you were still dismissed from your job.  I wasn't sure.  Something like the first instance happened to me at age 16.  I was put on Tofranil for depression and took it religiously, three times a day.  My doc did a blood level test and it showed (for some reason that is still not clear) that I had not taken the medication at all!  So he accused me of stockpiling the med to use in an overdose, which was certainly not the case.  He accused me of lying, in other words, so I took my business elsewhere.  It does happen