Health insurance doesn't always spare consumers from big health care bills.

Having done her homework, she was stunned to get a $10,000 bill from the surgeon.

"I panicked when I got that bill," said the 60-year-old retired civil servant who lives near Roseville, Calif.

Like Durocher, many consumers who take pains to research which doctors and hospitals participate in their health insurance plans can still end up with huge bills.

Sometimes, that's because they got incorrect or incomplete information from their insurer or health-care provider. Sometimes, it's because a physician has multiple offices, and not all are in network, as in Durocher's case. Sometimes, it's because a participating hospital relies on out-of-network doctors, including emergency room physicians, anesthesiologists and radiologists.

Consumer advocates say the sheer scope of such problems undermine promises made by proponents of the Affordable Care Act that the law would protect against medical bankruptcy.

"It's not fair and probably not legal that consumers be left holding the bag when an out-of-network doctor treats them," said Timothy Jost, a law professor at Washington and Lee University.

Adding insult to injury, insurers are not required to count out-of-network charges toward Obamacare's annual limit on out-of-pocket expenses.

Efforts by doctors, hospitals and other health providers to charge patients for bills not covered by their insurers are called "balance billing." The problem pre-dates the Obamacare and has long been among the top complaints filed with state insurance regulators.

Because the issue is complex and pits powerful rivals against one another among them, hospitals, doctors and insurers relatively few states have addressed it. What laws do exist are generally limited to specific situations, such as emergency room care, or certain types of insurance plans, such as HMOs.

See more here:

Even insured consumers get hit with surprisingly large medical bills