False Positives, Real Consequences: What the Quest Diagnostics Issue Reveals About Drug Testing Failures

In April 2025, a disturbing revelation emerged from California’s prison system: Quest Diagnostics, a major clinical laboratory, had used an “alternative reagent” in thousands of urine drug tests. This reagent caused a staggering spike in presumptive positive tests for opiates, tripling the usual rate. While Quest acknowledged the shift led to increased positive results, the company downplayed its significance and failed to inform those most directly impacted—incarcerated individuals who may have lost parole opportunities, faced disciplinary actions, or suffered setbacks in rehabilitation programs.

At Zendeh Del & Associates PLLC, a Texas-based law firm committed to defending civil rights and ensuring due process, this case underscores a much broader issue with profound implications: the systemic misuse of presumptive drug tests in legal settings.

The Scientific Flaw in Presumptive Testing

Presumptive drug tests, typically immunoassays, are designed as initial screening tools. They detect drug classes based on antibody reactions, which are prone to cross-reactivity. This means substances that are chemically similar to illicit drugs—like certain antibiotics, antidepressants, decongestants, or even poppy seeds—can trigger a false positive. Without follow-up confirmatory testing, such as Gas Chromatography/Mass Spectrometry (GC/MS) or Liquid Chromatography/Mass Spectrometry (LC/MS), these results are scientifically inconclusive.

Federal guidelines, including those from the Substance Abuse and Mental Health Services Administration (SAMHSA) and the Department of Health and Human Services, mandate confirmatory testing before a result can be reported as positive in workplace or federal drug screening. Yet, in criminal, family court, and probation contexts, presumptive results are often treated as final, leading to unjust outcomes.

Legal and Human Consequences

The consequences of relying on unconfirmed drug tests extend far beyond scientific error. For individuals entangled in the legal system, a single false positive can result in:

• Incarceration or denial of parole
• Loss of child custody or visitation rights
• Termination of employment or probation violations
• Damage to reputation and personal relationships

These outcomes are not hypothetical. More than 5,000 incarcerated individuals in California alone were affected by the Quest Diagnostics incident. Many may never be informed that their positive test was based on a faulty reagent.

Due Process and Drug Testing in Texas Courts

Here in Texas, presumptive drug tests are routinely used in courtrooms, probation offices, and child protective services. Family courts may remove children from parental custody based on these initial screens. Probation officers may file violation reports, triggering jail time. In some cases, these decisions are made without the benefit of confirmatory testing or expert interpretation.

This practice runs counter to the principles of due process and scientific reliability. Legal decisions must be based on sound evidence. When unconfirmed drug tests are used to make life-altering judgments, the justice system fails to uphold its most basic standards.

Best Practices for Attorneys and Legal Professionals

Legal professionals play a vital role in challenging the misuse of presumptive tests. Here are several steps attorneys can take to protect their clients:

Demand Confirmatory Testing: Never accept a positive immunoassay result at face value. File motions to compel GC/MS or LC/MS testing.

Engage Forensic Experts: Work with pharmacologists and forensic toxicologists who can explain the limitations of presumptive tests and identify possible sources of false positives.

Request Lab Documentation: Review chain-of-custody records, reagent lot numbers, and testing protocols to identify potential lab errors.

Educate the Court: Many judges and prosecutors are unaware of the science behind drug testing. Use expert reports and case law to educate the court on why confirmatory testing is necessary.

Challenge Improper Evidence: If a presumptive test is presented as conclusive, move to exclude it or request a Daubert hearing to challenge its admissibility.

Broader Implications for Reform

The Quest Diagnostics episode should serve as a wake-up call. We must demand transparency from laboratories and accountability from legal systems. This includes:

Requiring labs to disclose changes in testing reagents or protocols

Mandating confirmatory testing for all legal decisions based on drug screens

Creating standards for the use of drug testing in court proceedings

Providing training for judges, attorneys, and social workers on the limitations of drug tests

Advocacy and Awareness

At Zendeh Del & Associates PLLC, we advocate for science-based justice. We have seen firsthand how faulty testing can derail lives. Our firm supports legislative and policy changes that uphold due process and protect the rights of those facing allegations based on drug tests.

We urge all legal professionals to stay informed about developments in forensic science and to approach drug test evidence with the scrutiny it demands. When someone’s liberty or family is at stake, accuracy is not optional—it’s essential.

The misuse of presumptive drug tests is a systemic issue that affects thousands of lives. The recent revelations about Quest Diagnostics are not an isolated incident but a symptom of a larger problem. Legal systems must align with scientific standards to ensure fairness and justice.

If you are facing legal action based on a drug test, or if you represent someone who is, contact Zendeh Del & Associates PLLC. Our team is committed to challenging flawed evidence and fighting for the rights of every client.

Because in the pursuit of justice, there is no room for error.

Read the original article here