Although many employers are considering full-replacement high-deductible plan offerings or trying to increase enrollment in existing HDHPs, nearly half of all plans still have no in-network deductibles, according to the 2012 Medical Plan Trends Report by HighRoads and Corporate Executive Board.

"While the prevalence of HDHP plans has roughly tripled in the last five years, companies are still offering traditional PPO plans, many of which do not charge for in network visits," says Ania Krasniewska, senior director at CEB. "The absence of the right incentives and communications from organizations about the benefits of HDHP plans to individuals is driving employees to use these offerings that ultimately end up being significantly more expensive for organizations."

The study also reveals that the difference between in- and out-of-network costs employees experience has increased substantially since 2011. In fact, out-of-network primary care physician co-pays have become 53 percent higher than in-network co-pays as opposed to a difference of just 16 percent in 2011.