Well in a common urine drug test, the doctors cant usually differentiate between different types of benzodiazepines, as in the case of xanax (Alprazolam), it isn't actually detected in commonly performed drug tests which is an enzyme immunoassay screening test, as a separate drug from valium. It will just show up as a metabolite of benzodiazepines.
Now it actually depends on the lab which is performing the test for benzodiazepine whether a Liquid Chromatography Mass Spectrometry (LC/MS/MS) test has to be performed or not. If this test is done in addition to the screening test, then YES they can pick up on individual metabolites in the urine and determine whether you have valium or xanax or any other benzodiazepine for that matter.
Most labs will just do a simple screening test however in some labs a more comprehensive panel is done. Usually a more comprehensive testing panel is used for medical professionals etc. In cases like tests performed by pain management clinics or even in places where benzodiazepines are used more frequently like in psychiatrists offices, a more comprehensive panel can be performed to see exactly what you are taking.
So in short YES it is possible to detect different benzodiazepines in your system.
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