What I find interesting is flunking those kinda tests is sufficient for a probation or parole violation and go directly to jail. No bail. That seems an awful low burden of proof
Yeah, innocent until proven guilty and all of that....
Even the 'well established' field tests like the breathalyzer can give false positives- someone who is diabetic, using inhalers, or recently spent time working with solvents/paints.
Urinalysis using a GC and LC versus known standards is a lot more accurate. GC-mass spec or LC-mass spec or very accurate, but the equipment costs hundreds of thousands of dollars, and the personnel to run them aren't cheap either.