Quest Diagnostics says in a notice on its website, 'An update on an incident involving one of our systems', that it has identified an incident involving unauthorised access to its Quanum LSM system, which certain clients use to place test orders and receive and look up results.

Quest says it paused access to the system on discovery and is continuing to investigate, that its core business operations are not impacted, and that providers using direct-customer LIS interfaces or EMRs to order testing can keep doing so because those interfaces were not affected.

According to The Record (23 Oct), the system was taken offline on Thursday (22 Oct, US time); Quest's statement and FAQ say the company believes some patient data within the system was accessed; Quest is working with law enforcement and investigating what patient data was affected; customers can use paper requisitions in the meantime; and Quest said the incident did not involve the recent PHP vulnerabilities.

The Record says a Quest spokesperson declined to comment on the nature of the incident. Primary: Quest Diagnostics notice; wire: The Record.

UPDATE (24 Oct 2026): Quest's notice, now marked 'As of 8:00 am ET, October 23, 2026', adds FAQs. Quest says it believes some patient data within Quanum LSM was accessed and that, 'based on our investigation to date, personal information and patient records were affected'; it is still working to determine the specific data and the affected patients and providers, and as the covered entity will make notifications as required by applicable law, with letters describing resources including credit and identity monitoring.

Quest says there is no more access to Quanum LSM, that it is communicating with law enforcement, that no data was accessed in its Essential Insights and LabHQ systems although it paused access to them as a precaution, and that the incident is not related to a PHP programming language issue. Quanum LSM is redirecting clients to Quanum eLabs, where they can log in with the same credentials.

According to BleepingComputer (23 Oct), Quest said in a filing with the US Securities and Exchange Commission that it learned of the unauthorised access on 21 October 2026, and BleepingComputer could not find a threat group claiming the attack. (source: Quest Diagnostics; BleepingComputer)