Quest Diagnostics warns of potential data theft after attack on lab service system

A key system used by Quest Diagnostics to manage medical test results was taken offline on Thursday after the company discovered unauthorized access.

The company published a statement and an FAQ about the cyberattack, warning customers that they “believe some patient data” within the system was accessed. The platform, Quanum Lab Services Manager (LSM), is used to place test orders as well as receive and look up results. 

Access to the system has been paused while Quest investigates the attack. No other part of Quest has been impacted by the cyberattack but several other systems were paused as investigators probe the breach. 

Quest said it is working with law enforcement to resolve the incident and is investigating what patient data was affected by the attack. 

Customers can use paper requisitions in place of the system and Quest pledged to have Quantum back up and running by Friday. The company noted in the release that the incident did not involve the recent PHP vulnerabilities causing alarm among cybersecurity experts. 

A Quest spokesperson declined to comment on the nature of the incident. 

Quest is one of the largest clinical laboratory companies in the U.S., reporting more than $11 billion in revenue last year.

The New Jersey-based company says it serves half of the doctors and hospitals in the U.S. and one in three American adults each year.

No hacking group has taken credit for the incident as of Thursday afternoon. Quest is one of several healthcare testing firms to report cyber incidents in 2026. Baylor Genetics recently admitted that a data breach impacted more than 2.8 million of its patients and exposed lab results, medical testing information, Social Security numbers and more. 

Several other electronic health records companies dealt with attacks this year. 

In response to the attacks and several others over the last two years, Congress passed a bill this month expanding federal cyber requirements for healthcare organizations that handle patient data.