A company that performs medical tests at labs across the country is warning patients that their personal information may have been part of a massive data breach.

While many companies offer customers free credit monitoring after such incidents, Quest has not done so.

Quest Diagnostics says the breach involves the records of an estimated 11.9 million people.

American Medical Collection Agency, an agency Quest uses to collect delinquent accounts, reported that its database had been accessed by an unauthorized user last month. Quest, in a written statement, said it is seeking additional information from American Medical Collection Agency.

It is believed the unauthorized user had access to patients' personal and financial information, including Social Security numbers, as well as medical records. Quest says lab test results were not accessed.

"Quest is taking this matter very seriously and is committed to the privacy and security of our patients’ personal information. Since learning of the AMCA data security incident, we have suspended sending collection requests to AMCA," the statement said, in part.