Norfentanyl detection after negative confirmatory testing following heavy illicit fentanyl exposure: A two-patient...

Prolonged fentanyl detection may complicate urine drug testing (UDT). We describe norfentanyl detection after negative confirmatory testing.

Two patients (N = 2) entering residential treatment after heavy illicitly manufactured fentanyl exposure underwent clinically indicated serial UDT with confirmatory LC-MS/MS.

Both had negative confirmatory results followed by subsequent low-level urinary norfentanyl detection. Recurrent exposure could not be excluded.

These findings demonstrate diagnostic uncertainty rather than a defined pharmacokinetic mechanism.

Low-level norfentanyl after negative confirmatory testing should prompt longitudinal assessment rather than automatic attribution to recurrent use or prolonged detection.