A new audit finds that some UnitedHealthcare prescription drug plans didn't comply with certain Medicare rules, resulting in beneficiaries facing increased out-of-pocket costs and inappropriate denials or delays in accessing benefits.

The findings from an audit released earlier this month prompted the federal Centers for Medicare and Medicaid Services, or CMS, to issue a $2.5 million civil money penalty against the Minnetonka-based health insurer.

In a statement, UnitedHealthcare said it works closely with CMS to improve operations of its Medicare health plans.

"We immediately addressed the findings of this planned audit, which occurred last year, and remain committed to helping our members with the care they need, when they need it," the insurer said in a statement.

UnitedHealthcare is the nation's largest health insurer. It also is one of the nation's largest operators of Medicare health plans in which enrollees receive benefits through private health plans.

The new audit, which looked at UnitedHealthcare operations in May 2016, was one of 17 posted last week by CMS with fines ranging from $32,000 to UnitedHealthcare's $2.5 million penalty.

The government noted that, in most cases, fines would be larger for large insurers.

"The amount of the [civil money penalty] does not automatically reflect the overall performance," CMS said in a letter to insurers explaining audit results. The audits looked at how insurers complied with Medicare rules for "Part D" drug coverage, as well as broader questions of coverage determinations, appeals and grievances.

UnitedHealthcare, which is part of UnitedHealth Group, provides prescription drug benefits through stand-alone pharmacy plans, as well as health plans that cover medications as part of overall medical benefits.

Medicare has rules for how Part D plans manage their "formularies" of covered medications and how health plans use rules to regulate medicine usage by patients. The audit found systemic problems at UnitedHealthcare in complying with some of these rules, according to a CMS letter dated Nov. 22 that was posted March 1 on a government website.

"CMS identified violations of Part D formulary and benefit administration requirements that resulted in UnitedHealth's enrollees experiencing inappropriate denials of and/or delayed access to Part D prescription drugs at the point of sale," the letter states. It added that "some of the denials were for prescription drugs that are used to treat acute conditions that require immediate treatment."

Twitter: @chrissnowbeck