The 261 companies active in Medicare Advantage plans enrolled nearly 11.5 million Medicare beneficiaries as of March 2010, up 5.4% from March 2009, according to a new report.

The Medicare program, which encompasses Medicare health maintenance organization, preferred provider organizations, private fee-for-service plans and Medicare special needs plans, enjoyed a net gain of 620,834 new members from March 2009 to March 2010, says the report, published by Mark Farrah Associates, Kennebunk, Me.

The 5.4% growth rate was down from 12.6% growth for the same time one year ago, the report notes.

As of March 2009, there were 10 companies with more than 250,000 Medicare Advantage members. Today, only 8 companies have that distinction, the report says. Coventry, Blue Cross Blue Shield Michigan and WellCare all lost market share during the period. Currently, UnitedHealth Group and Humana together manage almost 33% of the market, up 3% from a year ago.

The full text of “Medicare Advantage Plans Peak at 11.5 Million Members” is in the Healthcare Business Strategy section of Mark Farrah Associates’ Web site.