A midstate chiropractor says he was forced to close his doors because of an ongoing financial feud with Highmark Inc., stemming from the health insurer's system for collecting money from doctors who, in Highmark's eyes, provide excessive or unwarranted care.

While his case is extreme, other Pennsylvania chiropractors are telling similar stories, saying Highmark has retroactively reneged on hundreds of thousands of dollars in reimbursements, forcing the chiropractors to come up with the cash if they want to stay in Highmark's good graces.

At the heart of the dispute is Highmark's system of auditing providers months or even years after it has already approved and paid for care. Insurers nationwide say that such vigilance is needed to cut down on fraudulent chiropractic billing and reduce the overall cost of care. Chiropractors say they're easily bullied because, unlike physicians or other specialists, they're often not affiliated with deep-pocketed hospitals.

Either way, it's a practice that is being utilized more than ever.

"They are definitely recovering more payments than they used to," said Mike Cassidy, an attorney specializing in health-care law with Pittsburgh law firm Tucker Arensberg.

Dan Carr closed his office in Elk County a year and a half ago, the victim, he says, of Highmark's system of flagging chiropractors who don't fall in line with the "back-crackers" who populate the field. Highmark conducted what's called a "post-payment audit" of Mr. Carr's records and services, and concluded that the recent work he's done doesn't merit reimbursement, either because the treatment was excessive, or his paperwork was deficient.

As a result, Highmark says Mr. Carr owes the insurer more than $430,000, a retroactive refund of the reimbursements Mr. Carr already had been paid.

"Needless to say, the ordeal has ruined my practice and knocked me down in life," said Mr. Carr. He hopes to reopen this year.

A spokesman for Downtown-based Highmark, Pittsburgh's dominant health insurer, said, "It's not our policy to comment on matters that are under consideration by the Highmark medical review committee."

Post- and pre-payment audits are tools insurers commonly use to make sure providers -- physicians, chiropractors and others -- are keeping adequate records, and billing for only medically necessary care. Those who aren't are considered "intensity outliers" or "over-utilizers," and it's these outliers that Highmark targets with its post-payment audits.

Mr. Carr's treatments were approved at first, then disapproved retroactively, making it difficult for the chiropractor to collect payment from a customer years after the fact. Because Mr. Carr hasn't repaid the $430,000 in reimbursement (and after he appealed Highmark's actions to the U.S. Department of Labor, alleging a violation of the federal Employee Retirement Income Security Act), Highmark began withholding reimbursements to Mr. Carr in 2005 as a way of collecting on the debt the company says it is owed. His patients were told via their benefits statements that Mr. Carr's services were "doctor paid." Highmark withheld $85,000 of the $430,000 before Mr. Carr closed his office, he says.

Mr. Carr says he was targeted because he's a black sheep. His practice promises to do more than straighten a back or ease the pain of sciatica -- he also is a certified strength and conditioning coach and says his treatments have helped people with foot and knee problems and rheumatoid arthritis. He also advertises "performance-enhancement" treatments that resulted in faster running, longer golf drives and "increased immunity from colds and flu."

But it's not just self-proclaimed "black sheep" who are subject to post-payment audits. Brenda Tomanek's Springdale Chiropractic also was hit by Highmark's auditing system, because in 2004, she prescribed exercise therapy more often than the average Highmark chiropractor. Office manager (and husband) Tom Courtenay says chiropractors are "easy targets, the low-hanging fruit."

Insurers keep an especially watchful eye on chiropractors and physical therapists, largely because of the repetitive nature of their services -- whereas a physician might see a patient twice a year, chiropractors might see the same patient weekly. Also, many insurers have been cracking down on chiropractors since a 2005 report from the U.S. Office of the Inspector General found that two-thirds of chiropractic claims filed with Medicare were deficient -- either due to record-keeping errors or a failure to validate the nature and duration of treatments.

"Medicare kind of sets the tone for everything that happens in the billing world," said Brian Kubit, of Plum.

But Mr. Courtenay said insurers use the Medicare report and fraud prevention as the guise for profiteering, citing a report that said post-payment refunds have grown from $10 million to $400 million industrywide since the 1990s. "They've found a new revenue stream," he said.

An audit works like this: Highmark asks for, say, 30 patient records and turns them over to a third party. That person reviews the records to determine whether Highmark should have paid the claims.

If the reviewer decides that 23 of the 30 records were deficient in some way and the claims shouldn't have been reimbursed, that 77 percent ratio is extrapolated across the whole of the business. So if Highmark had paid $130,000 in reimbursements to Mr. X over three years, it would ask for $100,000 of it back, post-payment, which just so happens to be the exact figure Springdale Chiropractic was asked to pay back.

"The extrapolation is a big threat," said the health care attorney, Mr. Cassidy, who has represented dozens of clients during Highmark and UPMC post-payment audits. "Numbers can go up astronomically."

Those astronomical numbers have led to a lawsuit from Springdale Chiropractic, said Mr. Courtenay, of York.

"You're basically accusing us of fraud," he said.

So far, Highmark has withheld $36,000 of the $100,000 owed by Springdale Chiropractic, which has spent $50,000 defending itself. "We're nearly bankrupt," he said.

In their case, he said, the third party who reviewed his records didn't say that treatments were medically unnecessary, but said that the office's records weren't thorough enough -- instead of noting that a patient's cervical vertebrae were manipulated, the third party said the office should have been noting specific bones.

"There's a certain amount of subjectivity" in determining which records are complete and which aren't, said Mr. Cassidy. The third-party reviewers are "independent, but they're obviously getting paid for what they do" and want to be rehired.

Most frustrating, the chiropractors say, is what they feel is a lack of recourse. The appeals hearing panel is filled with Highmark-picked doctors.

Mr. Carr has appealed to the state Department of Insurance, hoping for intervention on the grounds that the reimbursements were improperly denied. But last month, he received a letter that said: "At the present time, there is no Pennsylvania Insurance law that gives our Department jurisdiction over repayment requests made by insurance companies to medical providers or the contractual agreements between insurance companies and [providers]."

There are better ways of keeping costs down, says Mr. Kubit, who has a unique perspective on the issue -- not only is he a provider, but at one time he conducted audits for Medicaid, and he understands the need to fight systemic abuses.

Because all insurers now have sophisticated flagging and data-mining systems, he said, it would be easy for Highmark to intervene at the earliest signs of overutilization. The insurer could install a "corrective action" plan, telling the chiropractor what he'd done wrong and giving him time to fix it.

"If they're already profiling, give me a chance to shape up," he said, "or kick me out of the plan."