Quest Diagnostics is looking into the unauthorized access to its Quantum Lab Services Manager (LSM) system after discovering suspicious activity on October 21, 2026, with patient data files believed to have been exposed, and the number of impacted persons is still unknown.
The diagnostic testing company based in Secaucus, New Jersey shared about the incident when it submitted its Form 8-K filing to the U.S. Securities and Exchange Commission (SEC) on October 22, 2026. The company initiated an investigation to find out the nature and extent of the cyberattack.
Incident Response and Investigation
The system used by some Quest Diagnostics clients to send lab test orders, get results, and retrieve past issued results was affected by the incident. The company has temporarily blocked system access while the investigation is ongoing.
Third-party cybersecurity experts helped with the investigation. The initial investigation results show that the impact of the attack was limited to the LSM system. Knowing the extent of the unauthorized access is still in progress and Quest Diagnostics is still identifying the specific types of patient records affected. Hence, there is no exact number of affected individuals yet.
Upon discovery of the incident, Quest Diagnostics implemented measures to control the unauthorized activity. Remedial measures were activated to stop further unauthorized access to the impacted system. Quest Diagnostics has also alerted federal law enforcement authorities.
No threat group has publicly professed responsibility for the attack in the available report. The identity of the individual or group responsible has not been established.
Laboratory Services Continue During System Suspension
Quest Diagnostics reported that the cybersecurity incident did not interrupt its ability to provide patient services or affected its business operations. However, access to the LSM system was temporarily disabled as part of its response. Customers who normally use the affected platform have been provided with alternative methods for laboratory ordering and results delivery.
These alternatives include fax, paper-based processes, electronic medical records (EMRs), and direct-customer laboratory information system (LIS) interfaces.
The alternative arrangements enable customers to continue sending lab orders and getting test results even if access to the LSM system is suspended.
Previous Quest Diagnostics Data Breach
Quest Diagnostics had experienced a data breach in the past. It happened when hackers accessed American Medical Collections Agency (AMCA) systems from August 2018 to March 2019. The incident exposed PHI belonging to about 11.9 million Quest Diagnostics patients.
The present investigation involved a different system utilized by some Quest Diagnostics customers. The number of individuals affected by the October 2026 incident has not been established. Additional information will be released when available.
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