In April 2025, The Guardian reported that Quest Diagnostics used an “alternative reagent” in thousands of urine drug screens conducted within California prisons (https://www.theguardian.com/us-news/2025/apr/09/california-prison-drug-tests). This change, made without sufficient external disclosure, resulted in a dramatic spike in presumptive positive tests for opiates—tripling the usual rate. More than 5,000 incarcerated individuals may have been affected, many of whom were denied parole or had progress in rehabilitation programs questioned based on unconfirmed results. While Quest acknowledged the reagent caused higher presumptive positives, they downplayed its impact and failed to alert those most directly harmed by the error. It also begs the question: was this “alternative reagent” used by Quest Diagnostics outside the California prison systems?
This incident highlights a critical and ongoing issue across legal systems nationwide: presumptive drug tests, commonly immunoassays, are not definitive. These tests rely on antibody-based detection of drug classes and are highly susceptible to cross-reactivity with structurally similar legal substances—such as certain antibiotics, antidepressants, decongestants, or even food products like poppy seeds. Without confirmatory testing using mass spectrometry-based platforms like GC/MS or LC/MS, which precisely identify the chemical structure of specific drugs, these preliminary tests can—and often do—yield false positives. Yet in many criminal, family court, and probation contexts, these unconfirmed results are treated as conclusive evidence of drug use.
Scientific and forensic standards are clear: presumptive tests are screening tools, not diagnostic endpoints. They are intended only to flag specimens for further analysis, not to serve as a basis for legal action. Best practices outlined by the Substance Abuse and Mental Health Services Administration (SAMHSA) and the U.S. Department of Health and Human Services mandate confirmatory testing before a result can be reported as positive in workplace or federal testing programs. The failure to apply this same rigor in legal settings places individuals at serious risk of wrongful punishment or separation from their families—based on nothing more than a preliminary indication.
The real-world consequences of relying on unconfirmed test results are profound. A single presumptive positive can result in incarceration, the loss of child custody, employment termination, or reputational damage. In our work as pharmacologists and forensic toxicologists, we’ve encountered numerous cases where legal outcomes hinged on a test result that was never scientifically validated. This is not merely a technical oversight—it is a systemic failure to safeguard due process using reliable, evidence-based science.
If you are an attorney, public defender, or legal professional navigating a case involving drug testing results, we encourage you to engage an expert early. Understanding the difference between a presumptive screen and a confirmed analytical finding can dramatically shift the narrative of a case. Don’t let a flawed reagent or a misunderstood report dictate the outcome. Accurate interpretation matters—because liberty, family, and fairness depend on it.
Guest post written by:
Dr. Korin Leffler, PhD, MSEH – Expert Pharmacologist & Toxicologist
Dr. Rohan Parekh, PhD – Expert Pharmacologist, Chemist & Toxicologist