A confirmatory test is often ordered or reflexed when a positive drug screen is encountered, but not all positive DOA screens need to be confirmed. For example, if a patient admits to using THC and the urine THC test is positive, the clinician can stop there; there is no need to spend time and money confirming something that is not deemed suspicious. However, when a screen gives an unexpected result or when we need to know which particular drugs are present, as in the case of pain management, confirmatory testing is necessary.
Confirmatory testing is always performed using gas chromatography and mass spectrometry (GC/MS) or liquid chromatography with tandem mass spectrometry (LC-MS/MS). Unlike immunoassays, a GC-MS or LC-MS/MS instrument looks for specific chemical compounds. Mass spectrometry techniques can produce quantitative results, although not all laboratories report quantitative results. In most cases, the clinician is only looking for the identity of the drug and not the quantity.