Moody’s Investors Service has lowered the financial grades it has assigned to a large managed care company.

Moody’s, New York, has cut the rating on the senior unsecured debt of UnitedHealth Group Inc., Minnetonka, Minn., to Baa1, from A3.

Moody’s also has cut the insurance financial strength rating of the company’s United HealthCare Insurance Company unit to A2, from A1.

UnitedHealth still has a strong financial position and excellent cash flow, but it appears to be allowing the ratio of debt to capital to increase to about 40%, from the old level of 35%, Moody’s says.

UnitedHealth is using the increased leverage to pay for acquisitions, such as the recently announced agreement to acquire Unison Health Plans, Pittsburgh, and to buy back company stock, Moody’s says.

In related news, UnitedHealth announced that its UnitedHealthcare unit has completed the acquisition of Fiserv Health and related health operations from Fiserv Inc., Brookfield, Wis.