When David Brutman received a $3,000 bill for his wife's colonoscopy, he was angry and confused. He thought the cost would all be covered because under the Affordable Care Act most insurers must cover the full cost of preventive care such as check-ups, vaccinations and screenings.

It seemed straightforward enough, yet Brutman, a 41-year-old Silicon Valley entrepreneur, learned the hard way that the lines are easily blurred when it comes to determining whether services are considered preventive care or treatments that require payment.

"A lot of consumers don't know what's required, and a lot of doctors and pharmacists don't know what's required. Even insurance companies are working their way through a lot of it," said Judy Waxman, vice president of health and reproductive rights with the National Women's Law Center in Washington.

To avoid surprise costs, learn what is free and what is not and then take the time to think through the nature of your doctor visit, experts say. And if you've been billed incorrectly, there are steps you can take to correct the situation.

•Know the law: The Affordable Care Act requires most insurers to cover the full cost of many preventive services with no co-payments or other charges.

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That means vaccinations, cancer and other health screenings, annual well-visits, breast pumps and all FDA-approved contraceptives in most cases are available free of charge. The government features a list of preventive health services on its website, Healthcare.gov that should be cost-free.

Not everyone is eligible, however. Exempt are health plans that were in place when the law took effect on March 23, 2010. Always check.

•Understand the guidelines. The U.S. Preventive Services Task Force, a panel of primary care experts, sets specific guidelines that determine which medical services are considered preventive.

The key to full insurance coverage, however, lies in the details of the task force's recommendations. For example, although colonoscopies are a recommended preventive test, the guidelines state that it's for people 50 and older when recommended by a physician.

In Brutman's case, his wife, who is 41, took the test at her doctor's recommendation upon review of her family history. When the bill came, the insurer said it would cover the service because it was medically necessary but not at 100%, because she's not yet 50. The result for the couple was the $3,000 bill.

•Know your insurer's specific rules. Also important is to confirm how your insurer interprets the guidelines.

Mammograms, for example, are a recommended preventive exam for women over 40 every one or two years. In that case insurers have some discretion; one carrier may pay for the test annually while another will do so only every other year.

"Talk to your plan to learn about the details of what's covered. They are the one setting the rules," said Anthony Wright, executive director of Health Access.

Also remember to stay in your health plan's provider network. Once you see a doctor who doesn't participate with your plan, you'll be subject to costs, even if the visit is for a preventive service the law requires insurers to cover in full.

•Is your visit really preventive? Dr. Kurt Ransohoff, chief executive of Santa Barbara-based Sansum Clinic, says he increasingly sees people with high-deductible health plans wanting their medical complaints explored in the context of a preventive visit to avoid high out-of-pocket costs. But that doesn't always fly.

"Patients need to understand if they're just coming in for a checkup with nothing specific or major, it's probably preventive. If they're really coming in because they're wondering why their hip has been killing them for the last three months, that's something different," Ransohoff says.

Doctors typically know the difference, he said. "If you have to do more than a routine physical, you're supposed to bill it as an office visit in addition to a preventive visit." Ransohoff recommends that patients clearly state the purpose of their visit when making their appointment so that the patient and doctor are in agreement.

•Get to the bottom of unexpected bills. If you're sent a bill for a service you thought was preventive and covered in full, your first step is to call your doctor, says Cheryl Fish-Parcham, deputy director of health policy for Families USA, a healthcare advocacy organization in Washington, D.C.

Talk to the doctor's office about how the visit was billed "and then to the health plan about why it doesn't think it was preventive," she said.

In cases where a doctor's office or pharmacy is improperly billing, involve your insurer. Sometimes a customer service representative can get the provider on the phone and quickly clear up the confusion.