Quest Diagnostics confirms patient data breach in Quanum system

Quest Diagnostics confirmed that a cyberattack compromised patient personal and health data in its systems. The company learned of the incident on Wednesday, October 21, 2026, when a threat actor gained unauthorized access to its Quanum LSM system. The breach resulted in the exposure of certain patient records, including protected health information and personal data. Quest Diagnostics has not yet disclosed how many patients had information stolen during the attack.

The Quanum system is used by about half a million clinicians in thousands of locations across North America. In response to the incident, Quest Diagnostics deployed its incident response protocol to contain the activity and investigate the breach. The company notified law enforcement and is working with external experts to aid the ongoing investigation. Quest Diagnostics stated that it believes some patient records were exposed, though the full scope remains under review.

This is Quest Diagnostics' second known major data breach in a decade and the latest major cyber incident to affect the healthcare industry this year. The incident has not disrupted customer-facing operations. However, the company temporarily paused access to other systems, including Essential Insights and LabHQ, as a cautionary measure. Customers are recommended to use paper requisitions or Quanum eLabs to place orders while the Quanum LSM system is stopped.

Amanda Rivera, a spokesperson for Quest Diagnostics, did not answer questions about the incident. Following the disclosure of the breach, at least 19 class-action lawsuits were filed against the company.