‘Free’ screening? Know your rights to get no-cost care.

An ounce of prevention ... well, you know the rest. In medicine, prevention aims to spot problems before they worsen, affecting both a patient’s health and finances.

One of the more popular parts of the Affordable Care Act, which allows patients to get certain tests or treatments without forking out cash to cover copayments or deductibles, is based on that idea.

“There are still some gaps that need to be filled,” said Katie Keith, a researcher at the Center on Health Insurance Reforms at Georgetown University. But, she said, the law “unquestionably” made preventive care more affordable.

Since late 2010, when this provision of the ACA took effect, many patients have paid nothing when they undergo routine mammograms, get one of more than a dozen vaccines, receive birth control, or are screened for other conditions, including diabetes, colon cancer, depression, and sexually transmitted diseases.

» READ MORE: Colonoscopies save lives, but many Americans don’t get one. Home tests could help change that.

That can translate to big savings, especially when many of these tests can cost thousands of dollars.

Yet this popular provision comes with challenges and caveats, from an ongoing court case in Texas that might overturn it, to complex and obtuse qualifiers that can limit its breadth, leaving patients with medical bills.

Kaiser Health News spoke with several experts to help guide consumers through this confusing landscape.

Their number-one tip: Always check with your own health plan beforehand to ensure that a test, vaccine, procedure, or service you need is covered and that you qualify for the no-cost-sharing benefit. And, if you get a bill from a physician, clinic, or hospital that you think might qualify for no cost sharing, call your insurer to inquire or dispute the charge.

Here are five other things to know:

The law covers most types of health insurance, such as qualified health plans under the ACA that consumers have purchased for themselves, job-based insurance, Medicare, and Medicaid. Generally not included are pre-ACA legacy health plans, which were in existence before March 2010 and have not changed since then, and most short-term or limited-benefit plans.

Medicare’s and Medicaid’s rules on who is eligible for what tests without cost sharing may vary from those of commercial insurance, and Medicare Advantage plans in some cases may have more generous coverage than the traditional federal program.

The federal government currently lists 22 broad categories of coverage for adults, an additional 27 specifically for women, and 29 for children.

To get on those lists, vaccines, screening tests, drugs, and services must have been recommended by one of four groups of medical experts. One of those is the U.S. Preventive Services Task Force, a nongovernmental advisory group that weighs the benefits and potential drawbacks of screening tests when used in the general population.

For example, the task force recently recommended lowering the age for colon cancer screening to include people ages 45 through 49. That means more people won’t have to wait for their 50th birthday to skip copays or deductibles for screening. Still, younger folks might be left out a bit longer if their health plan applies to the calendar year, which many do, because those plans are not required to comply until January.

This area is also one in which Medicare sets its own rules that might differ from the task force’s recommendations, said Anna Howard, a specialist in care access at the American Cancer Society Cancer Action Network. Medicare covers stool tests or flexible sigmoidoscopies, which screen for colon cancer, without cost sharing starting at age 50.

There is no age limit on screening colonoscopies, although they are restricted to once every 10 years for people at normal risk. Coverage for high-risk patients allows for more frequent screening.

Insurers have leeway on what is allowed under the rules, but they have also been warned that they can’t be unwilling to spend the money.

California, for example, recently cracked down on insurers who were limiting cost-free testing for sexually transmitted diseases to once a year, saying that wasn’t adequate under state and federal laws.

The ACA does set parameters. Federal guidance says stop-smoking programs, for example, must include coverage for medications, counseling, and as many as two quit attempts a year.

With contraception, insurers must offer at least one option without copays in most categories of birth control but are not required to cover every single contraceptive product on the market without copays. For example, insurers could choose to focus on generics, rather than brand-name products. (The law also allows employers to opt out of the birth control mandate.)

As the ACA went into effect, trouble spots emerged. There was a lot of drama around colonoscopies. Initially, patients found that they were billed for copayments if polyps were found. But health regulators put a stop to that, saying polyp removal is considered an essential part of the screening exam. Those rules apply currently to commercial insurance and are still phasing in for Medicare.

More recently, federal guidance clarified that patients cannot be charged for colonoscopies ordered following suspicious findings on stool-based tests, such as those mailed to patients’ homes, or colon exams using CT scanners.

» READ MORE: Colonoscopy isn’t the only way to screen for colon cancer. Here are your options.

The rules apply to job-based and other commercial insurance with one caveat: They go into effect for policies whose plan years start in May, so some patients with calendar-year coverage may not yet be included.

At that point, it will be “a gigantic win,” said Mark Fendrick, director of the University of Michigan’s Center for Value-Based Insurance Design.

But, he noted, Medicare is not included. He and others are urging Medicare to follow suit.

Such differences in payment rules based on whether an exam is considered a diagnostic or a screening test are a problem for other types of tests, including mammograms.

Georgetown’s Keith pointed out a related complication: It might not be a specific development or symptom that triggers that change.

“If patients have a family history and need to get tested more frequently, that is often coded as diagnostic,” she said.

Dozens of vaccines for children and adults, including those for chicken pox, measles, and tetanus, are covered without cost sharing. So are certain preventive medicines, including certain drugs for breast cancer and statins for high cholesterol. Pre-exposure medications to prevent HIV — along with much of the associated testing and follow-up care — are also covered without cost to HIV-negative adults at high risk.

So, what’s next?

Overall, the ACA has helped lower out-of-pocket costs for preventive care, said Keith. But it has also attracted critics.

They include conservatives opposed to some of the free services, who filed the lawsuit in a Texas federal district court that, if it prevails, could overturn or restrict part of the law that provides no cost sharing for preventive care.

A ruling in that case, Kelley v. Becerra — the latest in a series of challenges to the ACA since it took effect — is expected in the coming weeks, and will likely be appealed.

If the ultimate decision invalidates the preventive mandate, millions of patients, including those who buy their own insurance and those who get it through their jobs, could be affected.

“Each insurer or employer would be left to decide which preventive services to cover and whether to do so with cost sharing,” said Keith. “So even those who did not lose access to preventive services themselves could have to pay out-of-pocket for all or some preventive care.”

Kaiser Health News is a nonprofit news service covering health issues.