False results in urine drug screening tests: Mechanisms, clinical interpretation and practical considerations

Introduction: Urine drug screening remains one of the most widely used toxicological testing modalities in clinical medicine, occupational health, forensic investigations, pain management, addiction medicine, and emergency care. The popularity of these tests is due to low cost, ease of specimen collection, rapid turnaround times, and relatively long detection windows for many substances. Despite these advantages, urine drug testing is associated with significant limitations. The most important of these limitations are false-results, which may lead to improper clinical decisions, legal consequences, workplace sanctions, and adverse patient outcomes. Most screening assays rely on immunoassay technology, which is designed to provide rapid presumptive results rather than definitive identification of drugs.
Methods: Based on the valid references, our review examines the scientific basis of urine drug screening, the leading causes of false-results, drug-specific considerations, and interpretation to improve diagnostic accuracy and patient care.
Results and Conclusion: Cross-reactivity with medications, metabolites, and endogenous compounds can produce false-positive findings, while assay limitations, specimen adulteration, dilution, timing of specimen collection, and restricted detection windows may result in false-negative findings. Understanding the mechanisms underlying erroneous results is essential for clinicians, laboratorians, and policymakers. Finally, confirmatory testing using GC-MS or LC-MS/MS should be considered mandatory whenever results are unexpected or associated with important consequences.