The first step to assessing whether someone has a drug in their system is often a urine drug screen.  Drug screens can be performed to test drug use after a crash, to test whether prospective employees are drug users, as part of compliance in a drug program, to determine possible impairment after a workplace accident, and in other civil and criminal situations.  Drugs of abuse typically tested are cocaine, methamphetamine, marijuana, phencyclidine, and morphine/opiates.  Urine drug screening detects whether certain drug classes are present, but generally cannot distinguish individual drugs.  So a test for morphine will also test positive for opiates, but not necessarily opioid medication. Advantages of urine drug screens are that they are inexpensive and non-invasive.  Other urine drug panels may be used to detect additional drugs in one class, or additional classes of medication.

Screens are used, and if positives are reported, they must be confirmed. Urine drug screens are based on immunoassay technology, in which the binding of antibody to a certain part of a molecule characteristic of a drug class will trigger a change in the amount of light at a certain wavelength that is given off and detected.  In other words, the more times an antibody binds to drug molecules, the more the assay signal changes.  However, the antibody targets only a particular part of the drug molecule, and so it will bind anything which has that particular chemical structure.  This leads to cross-reactivity and false positives.  For this reason, any test which has medical or legal consequences or would impact someone greatly should be confirmed by a GC/MS test, which is much more reliable in identifying individual drugs. In part to reduce the possibility of false positives, the measured drug concentration must exceed an established cutoffs/minimum level to register as a positive test result.

When evaluating these cases, it is important to obtain all the lab reports to verify that the analysis was correct in identifying the drug.  It is necessary to verify that the proper lab protocols were followed. The subject/employee, patient, etc should be asked if taking ANY medications, prescription, over the counter, or supplements, as these exposures may explain positive findings.  Questionable lab reports should be reviewed by knowledgeable experts to determine if the results are accurate and lab protocols and standards are followed.