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Sensitivity at screening + Specificity at confirmation

It’s not better to “de-sensitise” screening to avoid cross-reactivity. In safety-critical settings we want screening tools that cast a wide net, then use the laboratory to separate signal from noise. That’s how deterrence works in practice: screen broadly, confirm specifically.

Here’s why, in plain terms :

  • Screening and confirmation have different jobs. On-site oral-fluid screens are intentionally sensitive to pick up likely drug classes quickly. Labs then use highly specific methods (typically LC-MS/MS) to confirm the exact compound at defined thresholds. A screen that flags “possible amphetamine” and a lab that later reports “not confirmed” isn’t automatically a “false positive”—it’s the system doing its job. PMCScienceDirect
  • Amphetamine (AMP) screens are particularly prone to cross-reactivity. This isn’t a flaw unique to one brand; it’s a well-described property of the amphetamine immunoassay class. Structurally related medicines and designer stimulants can trigger an AMP class response, which is then ruled in or out at the lab. Several peer-reviewed studies and reviews document this behaviour. ScienceDirectOxford Academicjournals.pan.plPMC
  • Modern oral-fluid programmes are effective when they follow a two-step pathway. Large reviews and guidelines show oral fluid is a valid, non-invasive matrix for recent use—ideal for workplace risk management—provided screened non-negatives go to confirmation. International standards (e.g., SAMHSA’s Oral Fluid Mandatory Guidelines; AS/NZS 4760 ) are built around exactly this layered approach. PMC+1SAMHSAStandards New Zealand
  • About foods, vapes and “look-alike” chemicals. Biogenic amines in foods and some compounds in newer vaping products can, at times, nudge a sensitive immunoassay. That’s why we confirm at the lab with mass spectrometry, which targets the specific drug molecule and avoids class-based cross-reactivity. Emerging research continues to show complex e-liquid chemistry—another reason sensitivity at screening + specificity at confirmation is the right balance. PMC+1ACS Publications
  • Deterrence needs visibility. If we intentionally choose a less sensitive screen to avoid occasional cross-reactivity, we also risk missing genuine drug use—the very opposite of deterrence and safety. Evidence from method papers and device evaluations supports maintaining sensitivity at the screening step while relying on confirmation to resolve ambiguity. ScienceDirect+1
  • Role of OTC medications:Over-the-counter (OTC) medications are a common cause of false positives in drug tests. Nasal decongestants, sleep aids, and other common OTC medicines can contain substances such as amphetamines, opiates, and cannabinoids that may trigger a false positive. For instance, products containing ephedrine or pseudoephedrine, often found in cold and allergy medications, can yield false positive results for amphetamine type substances
  • One of the most common false positives is for amphetamines, which can be triggered by over-the-counter decongestants, the nasal inhaler Benzedrex, the antidepressant Wellbutrin, and the weight-loss supplement Acutrim.

Bottom line

  • Don’t blunt the net. Keep screening sensitive to maintain deterrence and capture potential risk.
  • Rely on the lab for certainty. Use confirmatory testing to separate true drug findings from cross-reactivity.
  • Follow the standard. Align policy with AS/NZS 4760 (and SAMHSA principles) so the process is fair, defensible, and effective. SAMHSAStandards New Zealand

Selected scientific references you can use to understand around cross reactivity

  • Immunoassay cross-reactivity (AMP):
    • Nieddu M. et al. Review of cross-reactivity in commercial immunoassays. ScienceDirect
    • Regester LE. et al. Designer drug cross-reactivity across five AMP assays. Oxford Academic
    • Pope JD. et al. False-positive AMP immunoassays—6-year study. PubMed
    • Hughey JJ. et al. Systematic evaluation of immunoassay cross-reactivity. PMC
  • Effectiveness of oral-fluid screening + confirmation:
    • Drummer OH. Drug Testing in Oral Fluid (review). PMC
    • Cone EJ. Interpretation of Oral Fluid Tests for Drugs of Abuse (review). PMC
    • Bassotti E. et al. LC–MS/MS confirmation method for oral fluid—rapid and compliant. ScienceDirect
    • SAMHSA. Oral Fluid Mandatory Guidelines—two-step framework (screen + confirm). SAMHSA
    • AS/NZS 4760:2019. Regional standard for oral-fluid collection, screening and confirmation. Standards New Zealand