For years, doctors have urged patients over the age of 50 to get colonoscopies to check for colorectal cancer, which kills 50,000 Americans a year. Their efforts were boosted last year by the federal health care law, which requires that key preventive services, including colonoscopies, be provided to patients at no out-of-pocket cost.

But there’s a wrinkle in the highly touted benefit. If doctors find and remove a polyp, which can be cancerous, some private insurers and Medicare hit the patient with a surprise: charges that could run several hundred dollars.

That’s because once the doctor takes action, the colonoscopy morphs from a preventive test into a treatment procedure.

The situation is causing confusion among doctors and the insurance industry. And it’s raising concerns among the American Cancer Society, the American College of Gastroenterology, and other physician and patient advocacy groups that consumers could be unprepared for the extra expenses, which can include deductibles, copayments and coinsurance. Medicare and at least two large private insurers, Kaiser Permanente, with 8.6 million members across the country, and Health Net, with 2.9 million members in several Western states, are charging the fees. Seven other major insurers said they would not charge enrollees.

Charging fees is “just dumb,” said Dr. Virginia Moyer, a pediatrics professor at Baylor College of Medicine who heads the U.S. Preventive Services Task Force, a panel of primary care experts that evaluates medical screening and preventive care. “We need to be sensible. It sounds like looking for a way not to pay for something.”

Adding to the uncertainty is the high-profile campaign by administration officials-including President Barack Obama and his wife, Michelle – to drum up support for the health law by highlighting the guarantee of free preventive care.  “If you join or purchase a new plan, the insurance company will be required to provide preventive care like mammograms, colonoscopies, immunizations, pre-natal and baby care without charging you any out of pocket costs,” the president wrote to supporters in an e-mail marking the six-month anniversary of the law.

Although colonoscopy is the most obvious example of the confusion, it is not the only one. Dr. Roland Goertz, president of the American Academy of Family Physicians, said it remains unclear how doctors and insurers are supposed to handle patient cost sharing for preventive checkups that turn up medical findings such as a skin lesion or breast lump needing a biopsy or excision during that visit. “Then it becomes a therapeutic visit,” he said. “Should this be a preventive visit with a modifying code, should it be considered only therapeutic, or should the patient be brought back for the needed care? It will take some clarification and time to work this through.”

Last July, the administration released regulations for insurers on the preventive care benefits. They prohibit health plans from imposing cost sharing for preventive services that were part of a visit to a doctor that was focused on prevention, if the services are not billed separately from the office visit. However, an insurer “may impose cost-sharing requirements for a treatment that is not a recommended preventive service, even if the treatment results from a recommended preventive service.”

Robert Zirkelbach, a spokesman for America’s Health Insurance Plans, said the colonoscopy issue illustrates the need for a clarification from administration officials about services such as colonoscopy where physicians provide both preventive and therapeutic care in the same visit. In written comments on the federal regulation last year, his group said physicians must understand how to appropriately code preventive services so that insurers know when to waive the deductible and coinsurance.

The federal health law specifies that insurers must fully cover services that have earned an A or B rating from the U.S. Preventive Services Task Force, plus immunizations recommended by the Centers for Disease Control and Prevention, and preventive care for women and children recommended by the federal Health Resources and Services Administration.

That coverage rule took effect last September. It applies to an estimated 31 million Americans in group health plans this year and 10 million in individual plans, and will cover 88 million by 2013.

To qualify for the free coverage, patients must go to providers in their health plan network.

Colonoscopy is on the U.S. Preventive Services Task Force’s recommended list, with an A rating, for all adults 50 and older. It checks for colorectal cancer, which is preventable with screening and highly treatable if caught early. A National Institutes of Health report last year said cost sharing likely affects people’s willingness to have such screening.

If a patient with no symptoms goes in for a screening colonoscopy and the gastroenterologist finds no pre-cancerous or cancerous polyps, everyone agrees that Medicare and commercial insurers are required to cover the expensive test 100 percent. But when the doctor removes a polyp, some insurers apply charges– meaning the insurer pays less of the bill.

Critics say charging cost-sharing defeats the purpose of the law. Studies show that colonoscopies find a polyp in at least 25 percent of men and 15 percent of women. Thus, many people face financial “post-procedure shock,” according to medical and consumer groups that are lobbying to stop insurers and Medicare from applying cost-sharing in this situation.

“We raised this with insurers and they wouldn’t budge,” said Dr. David Johnson, past president of the American College of Gastroenterology. Since the law took effect, “it’s still an ongoing problem,” he added.

Medicare is waiving the deductible for its beneficiaries but charges patients a copay of $186 plus 20 percent of the doctor’s fee, according to a Medicare spokeswoman.  She said there have been few complaints from beneficiaries about the policy.

In addition to Kaiser Permanente and Health Net, Regence BlueShield, which has 3 million enrollees in four Northwest states, initially said it charged members the deductible and coinsurance if a colonoscopy found and removed a polyp. But Regence spokeswoman Rachelle Cunningham subsequently said that was a mistake, there should be no cost sharing charges, and the company was “re-evaluating and re-processing some claims.”

A Health Net spokeswoman said that in an effort to help enrollees understand the situation, her company has trained its customer service staff to better explain colonoscopy coverage. Kaiser Permanente officials said the insurer “strongly supports” the health law’s guarantee of preventive services but when “services extend beyond preventive and require diagnostic or therapeutic services” the cost sharing will apply, depending on the specific plan details. (KHN is not affiliated with Kaiser Permanente.)

Aetna, Cigna, Group Health Cooperative, Humana, United Healthcare and Wellpoint/Anthem all said members pay no cost-sharing when a polyp is found. Assurant refused to comment.

This story was corrected on April 25 to reflect Dr. Moyer’s affiliation.