Drug Test Disaster? Quest Diagnostics Under Fire After False Positives in California Prisons

By Drug Test Digest Staff

If you thought eating a poppy seed muffin before a drug test was risky, wait until you hear what happened in California's prison system. In April 2025, The Guardian broke the story that Quest Diagnostics used an “alternative reagent” in thousands of urine drug tests—without notifying those tested or disclosing the reagent’s impact. The result? A surge in false positives for opiates, potentially derailing the lives of more than 5,000 incarcerated individuals. This incident comes on the heels of Quest’s own warning that drug-test cheating has hit a 30-year high across the workforce—read more in our report on nationwide cheating trends.

The new reagent reportedly tripled the usual rate of presumptive positives. For those inside, it wasn’t just a lab error—it was denied parole, revoked privileges, and damaged trust in an already fragile system. Meanwhile, questions around internal oversight have also surfaced—see how a Quest employee was accused of falsifying test results in our investigative update.

Presumptive Tests Aren’t Proof

The heart of the issue lies in the type of test used. Immunoassays—commonly used for initial drug screens—are notoriously susceptible to false positives. They can cross-react with everyday substances like cold meds, antibiotics, or yes, even poppy seeds. That’s why confirmatory tests like GC/MS or LC/MS are considered the gold standard. But in this case, many decisions were made before any confirmation ever occurred, raising questions about whether substitutes like synthetic urine could even fool the system. For an analysis of how well common alternatives perform under Quest’s protocols, check out our synthetic urine performance review.

Scientific Standards vs. Legal Practice

Federal programs and workplace drug testing follow strict protocols: no result is considered “positive” without confirmatory testing. Yet, in many legal settings—prisons, family court, probation—this standard often gets ignored. As the original article notes, preliminary results are treated as if they’re definitive, leading to major legal consequences from unvalidated data.

The Human Cost

This isn’t just a lab problem. It’s a people problem. A single erroneous result can separate a parent from their child, cost someone a job, or prolong incarceration. And with over 5,000 individuals affected in this incident alone, the scale of harm is staggering.

Experts like Dr. Korin Leffler and Dr. Rohan Parekh are urging legal professionals to get forensic experts involved early. Understanding the science behind a drug test result isn’t optional when someone’s future is on the line—it’s essential.

For more information, read the full article: False Positives, Real Consequences.