Use

Screening for drug abuse or use involving fentanyl and confirmation of fentanyl if present in the screen. The initial immunoassay provides a presumptive screen with high true-negative rate but potential for false positives due to cross-reactivity; a positive screen triggers confirmation by liquid chromatography tandem mass spectrometry (LC‑MS/MS) with quantification. Negative results indicate no fentanyl above ~0.20 ng/mL detected (screen cutoff: 2 ng/mL), while presence of fentanyl above 0.20 ng/mL or norfentanyl above 1.0 ng/mL indicates strong evidence of fentanyl use.