Samples that screen positive (at or above the cutoff) for target drugs, metabolites, or classes of drugs are considered presumptive positive and should be analyzed by a more specific methodology. Analytical methods developed and validated for gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) are employed by the vast majority of clinical laboratories to confirm the presence of specific drugs and/or metabolites.