Quest Diagnostics has confirmed that a threat actor gained unauthorized access to its Quanum LSM (Lab Services Manager) system, exposing patient records. The clinical laboratory company, which serves roughly one in three U.S. adults each year, disclosed the incident in a filing with the U.S. Securities and Exchange Commission.

According to the filing, Quest Diagnostics learned of the unauthorized access on October 21, 2026, and activated its incident response protocol to contain the activity, investigate its scope, and implement remediation measures. Quanum LSM is used by physicians, hospital staff, and medical office personnel to place test orders, retrieve results, and track order status.

The company says it is still investigating but believes some patient records were compromised. The specific categories of exposed data have not yet been determined. External security experts are assisting with the investigation, and law enforcement has been notified.

Operational Impact

Quest Diagnostics states that customer-facing operations have not been disrupted, and that users relying on direct-customer LIS interfaces or EMRs were not affected by the breach. As a precaution, the company has temporarily suspended access to additional platforms, including Essential Insights and LabHQ.

The Quanum LSM system itself has been taken offline. Quest Diagnostics is advising affected customers to use paper requisitions or its Quanum eLabs platform as alternatives for placing orders and retrieving results while the investigation continues.

No threat group has publicly claimed responsibility for the attack at this time.

History of Prior Incidents

Quest Diagnostics has faced major data exposure before. In 2019, the company disclosed that data belonging to approximately 11.9 million patients was compromised through a breach at third-party billing provider American Medical Collection Agency (AMCA). That incident triggered at least 19 class-action lawsuits, which were consolidated into multidistrict litigation that remains unresolved.

This latest breach adds Quest Diagnostics to a growing list of healthcare and diagnostics organizations disclosing significant data security incidents in recent months, underscoring continued targeting of the sector’s laboratory and records infrastructure.