“The guideline also emphasizes that targeted, definitive drug tests, such as those based on mass spectrometry technology, should be used as frontline drug screens whenever possible. Mass spectrometry-based tests overcome the limitations of the current frontline screening method, the immunoassay, which is useful but can produce a high rate of incorrect results and sometimes only reveals what general drug class is present in a patient’s urine rather than the specific drug.”

AACC Practice Guidelines for Lab Drug Tests