The researchers also found that the number of enrollees participating in HSA-eligible plans more than doubled in those five years, from 4% to 10%.

Correspondingly, the number of enrollees in the most dominant plans — PPO and POS plans — fell 10%, from 65% in 2013 to 55% in 2018. Save for a 6% bump in enrollment for HRA plans, enrollee shares of various other plans remained flat.

Paul Fronstin, director of research at the EBRI, said that costs are rising as employers see deductibles and cost-sharing as the easiest way to control overall spending.

"It's not surprising to me that deductibles are going up," Fronstin said. "All they're doing is changing one number in their plan, rather than excluding providers or certain drugs. It's the easiest thing to do."

The rise of HSA-eligible plans, Fronstin added, is a manifestation of the increased deductibles.

"They're then giving people an HSA which allows them to pay that deductible on a pre-tax basis," he said.

Other study findings include:

• Copays saw increases across the board with emergency visits rising the most (5%) and inpatient admittance rising the least (1%).
• Copays rose more among salaried individuals than non-salaried individuals.
• Copays rose more among non-union individuals.
• Coinsurance costs saw negligible increases.
• The average out-of-pocket maximums of $3,377 are still far below the statutory maximum of $7,350.

Read more: 

• 5 ways the CARES Act affects HSAs, FSAs and HRAs
• How HSAs help employees realize better 2020 tax breaks – and what to know for 2021
• What health care costs will look like post-COVID-19