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.

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.

KHN spoke with several experts to help guide consumers through this confusing landscape.