Quest Diagnostics discloses unauthorized access to patient records system

The company says it learned on October 21 that an unauthorized party accessed certain patient records through its Quanum LSM ordering system

Quest Diagnostics says it learned on October 21, 2026 that an unauthorized party gained access to its Quanum LSM system, which some clients use to place test orders and to receive and look up results. The company says it currently believes certain patient records were accessed, though it says the full scope of the incident is still under investigation.

Quest says it has notified federal law enforcement authorities and has brought in external cybersecurity experts to look into the breach. The company says the incident has not materially disrupted its business operations or its ability to serve patients.

The disclosure comes a day after Quest raised its full-year guidance for revenue, earnings per share and cash flow, citing strength across its physician, hospital and consumer channels. That breach now sits alongside an outlook that did not account for it, and it touches the same ordering and results system that runs through the channels management pointed to as growth drivers.

Quest says its operations have not been materially affected and that the scope of the breach is still being worked out, so the near-term financial impact is not yet clear. Past breaches in the healthcare sector have produced notification costs, litigation and regulatory scrutiny that unfold over quarters rather than days.