I recently spent a day on Capitol Hill with my fellow gastroenterologists to advocate for our patients. I told lawmakers about Mr. J, who recently turned 50 and, just as the U.S. Preventive Services Task Force recommends, looked into getting his first colonoscopy, a life-saving cancer screening.

But first, he had questions: Is the colon cleansing preparation really necessary? Does his wife have to take time from work to drive him home?  Are there less invasive options? If I get the colonoscopy,  will my insurance cover it?

That last one was the easiest to answer, I thought.  Yes, it will, I told him. Thanks to the Affordable Care Act, colorectal cancer screening, including colonoscopies and at-home stool tests, is covered at no cost to patients. Insurers are now required to fully cover the costs for any USPSTF recommendation that is deemed highly beneficial, and this is certainly one of them.

It is hard to convince patients to get a colonoscopy, so I was happy that cost was no longer part of the equation.

Two weeks later, Mr. J's colonoscopy went smoothly. We found and successfully removed two polyps.

A few weeks later, Mr. J got a bill for $500.  He called my office, furious.

He felt cheated. And so did I.

That's when I found out about the loophole.

This is how it works: A screening colonoscopy, done when a patient has no symptoms, is meant to look for polyps. If there are none, the procedure is billed as a diagnostic screening colonoscopy.

When we do find polyps, we remove them, because it's a simple matter in a patient who already is having a colonoscopy. This is also the reason this is a lifesaving test: We find and remove growths before they become cancerous.

But finding a polyp changes the billing code to a therapeutic colonoscopy, a reclassification that means it's not just a screening; it's an intervention. The new code means a bill is generated, and patients such as Mr. J were understandably outraged.

So were their physicians, and before long the Obama administration issued a clarification specifying that commercial insurers do not get to charge patients — not even a copay — simply because they got a polyp snipped out during a routine colonoscopy.

But that action didn't apply to Medicare, the government insurance for seniors and the disabled, and that's how Mr. J was covered.

There was nothing I could do to fix this for Mr. J, and he ultimately paid the $500.

I worry that the cost of this bureaucratic flaw is even higher.

Mr. J's polyps were precancerous, so he is at higher risk for cancer, and needs another colonoscopy in five years, not the 10 he could have waited if there had been no polyps. But will he return in five years?  Will he come to see me if he has concerning symptoms? Or has this loophole damaged his trust in me, specifically, and health care providers, generally?

Unfortunately, Mr. J is not alone – my colleagues have told me similar stories.

The American Gastroenterological Association, and other advocacy societies, have tried to address this issue with Medicare, but learned that it will take an act of Congress to fix it.  "The Removing Barriers to Colorectal Cancer Screening Act" is the legislation we need, but we don't know whether it will get the attention it deserves.

Preventing cancer is a bipartisan issue. But the legislators I met pointed out that the entire climate around health care is so messy, even noncontroversial bills like this are sitting on the shelf.  So while Congress is politicizing health care, Americans face a real barrier to cancer screening.  Our voices need to be heard, and patients need to be put first.

So, what are you waiting for?  When will you join us in demanding that your representatives fix this loophole, and provide free cancer screening, as the American people were promised?

Shazia Mehmood Siddique, M.D. is a third-year fellow in the division of gastroenterology at Penn Medicine, and is also a fellow at Penn's Leonard Davis Institute of Health Economics, and the Center for Healthcare Improvement and Patient Safety