Not many people are putting their money down yet, but the newest flavor on the health insurance shelf is getting plenty of lookers. Health Savings Accounts, or HSAs, are promoted by the Bush administration as giving consumers a stake in cost-cutting along with a chance to save for future health care needs. They're also attacked by some advocacy groups for increasing individuals' exposure to risk. About 3 million federal employees and retirees, along with private-sector workers, could soon consider whether to sample the new goods.

Created last December, HSAs are available only with policies that include high deductibles. A fund can include tax-exempt deposits of up to about $2,600 a year (about $5,150 for families) to pay for many health costs. These dollars can come from the covered individual, his employer or, as in the case of Aetna's plan for federal workers, the insurer.

About 10 percent of all employers are expected to offer the plans for 2005, according to David Cowles, a principal with benefits consulting firm Benemax in Medfield, Mass. Within the next two to five years, half of all firms are expected to follow, with some offering the plans as their only option, said Cowles. The plans are also available to people who don't qualify for employer-sponsored policies.

A Web site sponsored by a coalition of HSA providers and advocates, www.hsainsider.com, allows prospective buyers to compare plans based on premiums and other fees.

Businesses have reasons to promote these plans, say experts: "Many companies will now shift some costs to employees, lowering costs for employers, and the workforce will start to see the actual charges for medical care, which could make them become more cost-conscious and cost-saving health consumers," said Tom Billet, a senior benefits consultant for Washington-based benefits consulting firm Watson Wyatt.

And what benefits do consumers get? That depends partly on how much money you put into your HSA and how you choose to spend it. But there is an element of luck as well. You're betting that you won't get sick enough to exhaust the account and have to draw on other funds to pay for further care.

"Your ability to afford a catastrophe has to be factored in before opting for the new plan," said Gary Claxton, vice president at the Kaiser Family Foundation, which tracks insurance trends. "You'll want to be sure you have the resources, in and out of your HSA account, for out-of-pocket medical expenses, which can climb into the thousands, without affecting the way you live," said Claxton.

Under federal law, maximum liability for HSA policyholders is $5,000 for an individual, $10,000 for a family. Once you pay that out in premiums, expenses or coinsurance, 100 percent of eligible expenses are covered. Some insurers, including Aetna, set this cap lower. (See chart at right.) In comparison, the most you would generally pay out-of-pocket in a health maintenance organization (HMO), including premiums, is $2,000 for an individual, $6,000 for a family; for employees' most popular type of plan, a preferred provider organization (PPO), your spending maximum -- again, for eligible expenses -- is $2,500 for an individual, $7,000 for a family.

For the healthiest workers -- those with no regular drug costs or doctor visits other than covered preventive care -- HSAs pose a clear advantage: Premiums can be as much as 40 percent lower than those for other plans, and you can sock away money during your healthy years to fund future medical expenses. For less healthy workers, outcomes are less predictable.

Should you investigate HSAs? Definitely. Opt for one of them? That's a tougher call.

Many HSA plans include no-extra-charge preventive care such as an infant checkups and mammograms, but your HSA funds can pay for all other medical expenses, from antibiotics to chemotherapy, until you exceed the deductible (at least $1,050 for singles, $2,100 for families). At that point, you'd pay coinsurance, generally about 20 percent of costs, for additional care until your reach the out-of-pocket maximum.

The theory is that consumers with HSAs may change their habits after seeing actual medical charges rather than much smaller co-payments, said Billet. For example, an emergency room visit for a nasty cough would take about $380 from their personal account, according to the Blue Cross Blue Shield Association. Prozac would cost them about $225 a month from Drugstore.com, while the generic formulation of the antidepressant costs about $65.

Let's say that you buy a family plan with a $5,000 deductible, that you designate $3,000 for your HSA and that you use all that HSA money to cover doctor visits, blood tests, physical therapy sessions and the like. In that event, you'll have to pay the next $2,000 in medical expenses yourself. Then after you've met the deductible, the insurance plan kicks in, paying all or most of your approved medical expenses, depending on your plan's provisions.

"One risk, of course," said Ron Pollack, head of the Washington advocacy group Families USA, "is that a patient might forgo necessary medical care, opting to save the money, until the problem becomes more serious, and much more expensive."

Another risk, he said, is that healthier consumers will choose HSAs, leaving an older and sicker pool behind. "Without a younger, healthier pool of people among whom to spread risk, I'd expect to see insurance premiums skyrocket among older, sicker consumers over the next few years," Pollack said.

A Good Plan for You?

Before you commit, it's a good idea to read through the list of frequently asked questions (www.opm.gov/hsa/faq.asp) posted by the federal Office of Personnel Management. Even if you work in the private sector or are shopping for an individual policy, the questions should prepare you for a talk with your agent or your employer's benefits staff. This is especially important for individual policy buyers, since they'll likely be dealing with salesmen who may biased toward their own product.

Here are some reasons you may find an HSA tempting:

* You own the money in the account even if you retire or change plans or employers.

* Tax-free withdrawals may be made for expenses such as prescription drugs, a doctor visit for a sinus infection, setting a broken arm and physical therapy prescribed by a doctor. (See the IRS list at www.irs.gov/publications/p502/ar02.html#d0e516.)

* Unused funds and any interest they've earned can be carried over, without limit, from year to year. (You can even spend set-asides on nonmedical expenses. But do that before age 65, and you'll pay income tax on the funds used plus a 10 percent penalty.)

* Contributions to an HSA by your employer, your insurer or yourself are not considered income on which you owe federal taxes. If your employer doesn't allow pretax payroll deductions for your HSA, you may choose to fund your account with after-tax dollars and then claim an offsetting deduction when you file your annual tax return.

Some benefits experts, like Greg Scandlen, a senior fellow at the nonprofit National Center for Health Policy Analysis, say all consumers can realize savings with HSAs, because of their tax advantages and the lower premiums that come with high-deductible insurance. But others worry that people who don't adequately fund an HSA will find it hard to meet the deductible and even harder to afford the coinsurance bills they will face before reaching the annual cap on-out-of-pocket obligations.

Break your leg on a ski trip, for example, and your HSA could be quickly drained by two surgeries and months of physical therapy. That could be the case even if you negotiate the fees and services tied to surgery, anesthesia and other services -- a habit it may be prudent to cultivate. But shopping around for quality care can be difficult -- especially when it involves emergency care or other unanticipated needs.

On top of that, deposits into the account may be spread out over the entire year. As a result, if you incur major expenses in February, you may have to pay out of pocket, or out of credit card, until the plan reimburses you.

"These are risk-oriented plans," said the Kaiser Family Foundation's Claxton. "Keeping yourself healthy [by doing things] such as keeping weight down and getting exercise means you're less likely to have to shell out for heart surgery or diabetes medicines down the road. But the plans are not at all sympathetic to accidents, and that's an expense you just can't predict."

Planning Ahead

But there are some predictions you can make, and many firms, including Aetna, are offering online calculators to help you track past expenses and predict future ones. Aetna, together with the Financial Planning Association, a trade association for financial planners, has put together some online decision-making tools that can help you sort through your options.

For example, the site has an excellent list of options you should look for in your plan (www.planforyourhealth.com/careers_rank.cfm). But bear in mind that the information Aetna presents is likely to put HSAs in a favorable light.

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Francesca Lunzer Kritz wrote about health insurance options for last year's special Open Season issue of the Health section.