DRUG TESTING: PRESUMPTIVE vs DEFINITIVE

DEFINITIVE TESTING

Presumptive vs Definitive


PRESUMPTIVE vs DEFINITIVE


Traditional workplace drug testing involves either single presumptive testing, where specimen is subjected to an initial presumptive test (commonly referred to as screening), or binary reflex testing, where the initial screen is followed by a definitive test (commonly referred to as confirmation).



“Presumptive” (Rapid Tests) refers to the limitation on reporting specific parent or metabolite.

Presumptive tests include immunoassays and POCT Immunoassay Screening

  • Drug class specific reaction based upon validated cut off levels
  • “Qualitative” meaning either a positive (if at or above cut off) or negative if below
  • Susceptible to “false positive” reactions e.g. reacting to similar chemical looking compounds
  • Also potential for “false negative” reactions e.g. level of parent or metabolite below ability for specific class/panel to react

POCT (Rapid Test)

  • Provides fast results based upon a broad range of potential compounds that can react with the panel[AM1]
  • Most commonly used in workplace and/or employment testing
  • Significant limitations include false positive/negative results, non-descript qualitative results that do not confirm/deny presence of a specific medication
  • Limitations include QC of testing devices, testing protocols and device interpretation by undertrained staff

“Definitive” testing addresses this limitation.

  • Definitive Testing can be performed on the following platforms: gas-phase chromatography/mass spectrometry (GC/MS), liquid chromatography tandem mass spectrometry (LC/MS/MS) and high-resolution liquid chromatography tandem mass spectrometry (HR-LC/MS/MS).
  • HR-LC/MS/MS Testing May be used for initial definitive screening and/or confirmation.
  • HR-LC/MS/MS = “Gold-Standard” for pre-employment and post-accident testing.

Ability to match compound specific confirmation menu and cutoff

  • Lower incidence of false negatives compared to traditional tests via
  • Lower screening cutoffs afforded by sensitive instrumentation
  • Selective detection by MS technology not dependent on cross-reactivity