Prolonged Fentanyl Detection on Urine Drug Testing: A Case for Revising Interpretation Frameworks in the Setting of Chronic Use.

Abstract

Urine drug testing (UDT) plays a central role in monitoring substance use during pregnancy and the postpartum period, with results carrying significant legal and social consequences, including family separation. We present 2 cases of individuals with opioid use disorder who continued testing positive for fentanyl on UDS for 170 and 210 days, respectively, after their last reported use. Both cases involved a fentanyl cutoff threshold of 0.5 ng/mL. In case 1, a 33-year-old male remained intermittently positive for 170 days, with fentanyl levels ranging from 0-7.1 ng/mL. In case 2, a 33-year-old female remained intermittently positive for 210 days, with fentanyl levels ranging from 0-1.9 ng/mL. Both individuals maintained low but detectable fentanyl concentrations throughout this extended period. These prolonged positive results delayed child custody reunification for both families. Despite mounting evidence of prolonged fentanyl detection, many agencies continue to rely on outdated guidelines suggesting fentanyl persists for only 1-3 days after last use. Without national standards for fentanyl detection window cutoffs, individuals maintaining abstinence continue to be suspected of recent use based solely on positive UDT results. We urge clinicians and child welfare professionals to consider these extended detection windows when interpreting positive fentanyl tests and to avoid misattributing persistently low positive results to recent drug use. These findings underscore the urgent need to revise decision-making frameworks to prevent harm to families and ensure appropriate clinical and legal outcomes.