When Kristy Uddin, 49, went in for her annual mammogram in Washington state last year, she assumed she would not incur a bill because the test is one of the many preventive measures guaranteed to be free to patients under the 2010 Affordable Care Act. The ACA’s provision made medical and economic sense, encouraging Americans to use screening tools that could nip medical problems in the bud and keep patients healthy.

So when a bill for $236 arrived, Uddin — an occupational therapist familiar with the health care industry’s workings — complained to her insurer and the hospital. She even requested an independent review.

“I’m like, ‘Tell me why am I getting this bill?’” Uddin recalled in an interview. The unsatisfying explanation: The mammogram itself was covered, per the ACA’s rules, but the fee for the equipment and the facility was not.

That answer was particularly galling, she said, because, a year earlier, her “free” mammogram at the same health system had generated a bill of about $1,000 for the radiologist’s reading. Though she fought that charge (and won), this time she threw in the towel and wrote the $236 check. But then she dashed off a submission to the KFF Health News-NPR “Bill of the Month” project:

“I was really mad — it’s ridiculous,” she later recalled. “This is not how the law is supposed to work.”

The ACA’s designers might have assumed that they had spelled out with sufficient clarity that millions of Americans would no longer have to pay for certain types of preventive care, including mammograms, colonoscopies, and recommended vaccines, in addition to doctor visits to screen for disease. But the law’s authors didn’t reckon with America’s ever-creative medical billing juggernaut.

Over the past several years, the medical industry has eroded the ACA’s guarantees, finding ways to bill patients in gray zones of the law. Patients going in for preventive care, expecting that it will be fully covered by insurance, are being blindsided by bills, big and small.

The problem comes down to deciding exactly what components of a medical encounter are covered by the ACA guarantee. For example, when do conversations between doctor and patient during an annual visit for preventive services veer into the treatment sphere? What screenings are needed for a patient’s annual visit?

A healthy 30-year-old visiting a primary care provider might get a few basic blood tests, while a 50-year-old who is overweight would merit additional screening for Type 2 diabetes.

Making matters more confusing, the annual checkup itself is guaranteed to be “no cost” for women and people age 65 and older, but the guarantee doesn’t apply for men in the 18-64 age range — though many preventive services that require a medical visit (such as checks of blood pressure or cholesterol and screens for substance abuse) are covered.

No wonder what’s covered under the umbrella of prevention can look very different to medical providers (trying to be thorough) and billers (intent on squeezing more dollars out of every medical encounter) than it does to insurers (who profit from narrower definitions).

For patients, the gray zone has become a billing minefield. Here are a few more examples, gleaned from the Bill of the Month project in just the past six months:

Peter Opaskar, 46, of Texas, went to his primary care doctor last year for his preventive care visit — as he’d done before, at no cost. This time, his insurer paid $130.81 for the visit, but he also received a perplexing bill for $111.81. Opaskar learned that he had incurred the additional charge because when his doctor asked if he had any health concerns, he mentioned that he was having digestive problems but had already made an appointment with his gastroenterologist. So, the office explained, his visit was billed as both a preventive physical and a consultation. “Next year,” Opasker said in an interview, if he’s asked about health concerns, “I’ll say ‘no,’ even if I have a gunshot wound.”

Kevin Lin, a technology specialist in Virginia in his 30s, went to a new primary care provider to take advantage of the preventive care benefit when he got insurance; he had no physical complaints. He said he was assured at check-in that he wouldn’t be charged. His insurer paid $174 for the checkup, but he was billed an additional $132.29 for a “new patient visit.” He said he has made many calls to fight the bill, so far with no luck.

Finally, there’s Yoori Lee, 46, of Minnesota, herself a colorectal surgeon, who was shocked when her first screening colonoscopy yielded a bill for $450 for a biopsy of a polyp — a bill she knew was illegal. Federal regulations issued in 2022 to clarify the matter are very clear that biopsies during screening colonoscopies are included in the no-cost promise. “I mean, the whole point of screening is to find things,” she said, stating, perhaps, the obvious.

Though these patient bills defy common sense, room for creative exploitation has been provided by the complex regulatory language surrounding the ACA. Consider this from Ellen Montz, deputy administrator and director of the Center for Consumer Information and Insurance Oversight at the Centers for Medicare & Medicaid Services, in an emailed response to queries and an interview request on this subject: “If a preventive service is not billed separately or is not tracked as individual encounter data separately from an office visit and the primary purpose of the office visit is not the delivery of the preventive item or service, then the plan issuer may impose cost sharing for the office visit.”

So, if the doctor decides that a patient’s mention of stomach pain does not fall under the umbrella of preventive care, then that aspect of the visit can be billed separately, and the patient must pay?

And then there’s this, also from Montz: “Whether a facility fee is permitted to be charged to a consumer would depend on whether the facility usage is an integral part of performing the mammogram or an integral part of any other preventive service that is required to be covered without cost sharing under federal law.”

But wait, how can you do a mammogram or colonoscopy without a facility?

Unfortunately, there is no federal enforcement mechanism to catch individual billing abuses. And agencies’ remedies are weak — simply directing insurers to reprocess claims or notifying patients they can resubmit them.

In the absence of stronger enforcement or remedies, CMS could likely curtail these practices and give patients the tools to fight back by offering the sort of clarity the agency provided a few years ago regarding polyp biopsies — spelling out more clearly what comes under the rubric of preventive care, what can be billed, and what cannot.

The stories KFF Health News and NPR receive are likely just the tip of an iceberg. And while each bill might be relatively small compared with the stunning $10,000 hospital bills that have become all too familiar in the United States, the sorry consequences are manifold. Patients pay bills they do not owe, depriving them of cash they could use elsewhere. If they can’t pay, those bills might end up with debt-collection agencies and, ultimately, harm their credit score.

Perhaps most disturbing: These unexpected bills might discourage people from seeking preventive screenings that could be lifesaving, which is why the ACA deemed them “essential health benefits” that should be free.

KFF Health News is a national newsroom that produces in-depth journalism about health issues and is one of the core operating programs at KFF—an independent source of health policy research, polling, and journalism. Learn more about KFF.

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