Samples that screen positive, those above the cutoff, are usually considered presumptively positive. Many labs then reflex these positive samples for confirmatory testing, which uses more specific methodologies. Most clinical laboratories employ gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) to confirm the presence of specific drugs and/or metabolites.
Note: It is important to remember that a negative drug screen does not necessarily mean that no drug was present. This means that the drug was not detected above the cutoff.
