Hello,
Thanks for posting,
There are few laboratories in the world that are actually not up to standard and most of them use expired reagent and non-experienced technicians. I think you should find out from other clients of that hospital if they have had similar false-results experiences from the same lab.
It is possible in some cases, while you are on certain prescription drugs to have a certain amount of illicit substance in your system, but I hardly know of any drugs that is a derivative of marijuana that is being used as a prescription drug. The drugs you have mentioned do not contain marijuana or its derivatives but a drug such as
norco contains hydrocordone which is an
opiate derivative and you could test positive for
opium not marijuana. It is also possible, that if you live with somebody that often smokes marijuana, it might also be found in your blood stream but in very small concentrations.
The laboratory has as obligation to redo a test if it is contested by either the doctor or the patient and I see no reason why they insist after 1 testing that the results are definite.
Also, you should not forget that you have the freedom to select another clinic, another
primary care doctor and another laboratory if you do not feel comfortable with your present situation. I do suggest, however, that you discuss with your primary care physician about this situation that is obviously bothering you and see if the test can be re-conducted.
Hope this helps and wish you the best