Recent Growth In Medicare Advantage Enrollment Associated With Decreased Fee-For-Service Spending In Certain US Counties.

Recent increases in Medicare Advantage enrollment may have caused lower spending growth in the fee-for-service (FFS) Medicare population. We identified the counties of largest Medicare Advantage growth and determined if increased enrollment was associated with reduced FFS Medicare spending growth in those counties. We found that 73 percent of counties experienced at least a 5-percentage-point increase in Medicare Advantage penetration between 2007 and 2014, with the most growth occurring in larger and poorer counties in the Northeast and South. The association between Medicare Advantage growth and FFS Medicare costs varied depending on baseline Medicare Advantage penetration: In counties with low baseline penetration, Medicare Advantage growth did not have a significant effect on per capita FFS Medicare spending, whereas in counties in the highest quartile of baseline Medicare Advantage penetration, it was associated with a significant decrease in FFS Medicare spending growth ($154 annually per 10-percentage-point increase in Medicare Advantage). These findings suggest that Medicare Advantage growth may be playing a role in moderating FFS Medicare costs.