That which walks like a duck, and talks like a duck, is not always actually a duck.

That's the argument the American Medical Association has been using for decades to block public access to doctors' Medicare billing records. The AMA worries that people and the press will misinterpret the numbers when they see how doctors bill the government's $500 billion health care program for the elderly and disabled, and that doctors who are doing nothing wrong could be unfairly accused of fraud.

But the medical association lost that argument last month and now doctors' Medicare billing data is a matter of public record – dense, complicated records. And those records are beginning to tell stories.

KQEDand the independent newsroom ProPublica took a look a close look at one particular type of medical service in the data.

In order to get paid, doctors have to label everything they do for a patient with a billing code. Routine visits for established patients are billed on a scale of 1 to 5. A level 1 code is for a short, easy office visit; level 5 is meant for the longest, most complicated office visits, which are also paid at a higher rate.

Office visits account for about $12 billion in Medicare spending every year.

One emergency medicine physician in Newhall, California, Dr. Gary Ordog, billed Medicare for a level 5 visit an average of 30 times per patient in 2012. A number that high raises "huge red flags, really high in the sky, waving their arms ferociously!" says Patrice Morin-Spatz, a specialist in medical coding and reimbursement.

The more typical doctor in California bills for only one or two of these high-level visits per year for each patient. Morin-Spatz says when she sees doctors with coding practices like Ordog's, she thinks one thing: "I think that they are trying to code based on how much money they want, as opposed to coding with a goal to satisfy the requirements of each particular level of service."

California's medical board has tried to revoke Ordog's medical license for what it called "incompetence, making false statements, and inadequate record keeping." He is still practicing, but currently on probation, and did not return multiple requests for comment.

Ordog is one of hundreds of doctors in California with unusual billing patterns. In fact, three California physicians are among the top five nationally in billing for the highest number of complex, "level 5" office visits. Nationwide, some 1,800 doctors always billed at the highest level possible for routine office visits.

In Colorado, 71 doctors billed at the highest possible level for every one of their Medicare office visits. NPR tried to contact 15 of these physicians. Most didn't return the phone calls, but Dr. Marilyn Levi did. She's director of transplant infectious disease at the University of Colorado in Denver.

Levi works in the only academic medical center for hundreds of miles in any direction. It's where other hospitals in the region send some of their toughest patients.

"And therefore," Levi says, "the time that is required to take care of them is longer than [for] some of the other specialties in infectious disease ... and that results in the higher coding."

That sort of context isn't obvious in the huge trove of Medicare payment data that was made public for the first time last month. Levi is concerned people will misinterpret the information.

"There has to be an understanding and recognition of specialty care that is provided in only a few places," she says. "So I think it's dangerous to lump everyone together and base everything on a code."

Dr. Aris Sophocles, a Denver physician who teaches medical coding to medical students and doctors, says that's a perfectly reasonable caution. But not every doctor who frequently bills at the highest level is being honest, he says.

"When I see someone in family medicine, I get suspicious," says Sophocles. "Similarly, in other specialties, such as general internal medicine and gastroenterology, I become suspicious."

Sophocles is hardly on a witch hunt. In fact, he's also an attorney, and he helps defend doctors who get prosecuted for having fishy-looking billing practices. He says Medicare does audit doctors, and some have had to pay Medicare back, or even face jail time, which causes them to err on the side of under-coding — charging less than perhaps they should.

"Some, though, are either unaware or unafraid," he says. "And they tend to over-code anyhow, and the release of this database may indicate who those people are."

In a statement to ProPublica, Medicare officials said that "it would be highly unusual" for doctors to bill at the highest level 100 percent of the time.

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