(Bloomberg) — DaVita HealthCare Partners Inc. received a subpoena from U.S. authorities seeking patient-diagnosis documents from the past seven years as part of what the company said is a broader probe into abuses in Medicare.

The Department of Health and Human Services requested paperwork dating back to January 2008 relating to diagnosis coding, risk adjustments, and payments, the Denver-based provider of health services said Wednesday in a regulatory filing. Some of the data requested is tied to a "potentially improper" practice by HealthCare Partners that ended after DaVita acquired that company in late 2012.

As disclosed in financial statements this year, "we notified the U.S. Center for Medicare & Medicaid Services of the legacy coding practice and potential overpayments," DaVita said. "The company is cooperating with the government and will gather and produce the requested information."