As health care open enrollment gets underway at many workplaces, employees should do their homework when signing up for plans that offer health savings accounts, new research suggests.

Health savings accounts, or HSAs, are offered only in tandem with specific high-deductible health plans, which are becoming more prevalent as employers seek to manage costs. The lofty deductible — at least $1,300 for an individual and $2,600 for a family — means that workers pay more for medical care out of pocket before insurance pays.

The plans can be a boon for workers who understand how to take advantage of the tax benefits that HSAs offer. (The money is tax-free as long as it's spent on eligible health care, and workers take the money with them if they switch jobs.) But there may be caveats.

A new analysis by the Employee Benefit Research Institute found that while workers overall in a health plan with an HSA visited the doctor less often for nonpreventive care, the decline was more than twice as large for workers who made $50,000 or less, compared with those who made $100,000 or more.

Lower-income workers were also more likely to reduce their use of preventive services, like flu shots and breast cancer screenings, even though such services aren't subject to the deductible.

The study focused on more than 150,000 workers at a single large employer over six years.

Paul Fronstin, an author of the study, said although HSAs had been around for more than a decade, they are complex and new to many workers.

"It just takes some time, to understand how their benefits work," he said.

Alison Galbraith, an assistant professor at Harvard Medical School, said lower-income patients may avoid free preventive care because they don't understand the details of their policies.

"The plans are complicated," she said, "and they may not be sure what's covered."

It's also likely, she said, that because they may avoid office visits, in general, to avoid incurring costs, lower-income workers are less likely to be reminded to follow up with free services, like immunizations. And they may be concerned that while visiting a doctor for a covered screening, they may also end up with extra care that's not covered.

So should lower-income workers avoid HSA plans if they have a choice?

Not necessarily. Monthly premiums are usually lower with such plans, and employers often make contributions to HSAs that can help cover the cost of care. The typical contribution by large employers to an HSA is $600 for an individual and $1,100 for family coverage, said the National Business Group on Health.

To encourage workers to get preventive care, some employers attach strings to their contributions, said Steve Wojcik, vice president of public policy with the business group. They may, for instance, require workers to designate a primary care physician or complete recommended no-cost screenings.

It may make sense, Fronstin said, for employers to base HSA contributions on a worker's income, so lower-income employees would receive more funds to help cover costs.

In the meantime, he advised, workers should read health plan documents carefully and contact their human resources department to clarify anything that's confusing.

Ann Carrns writes for the New York Times.