Ever since Noriko Hunter, an internist in Sterling, started receiving letters from insurance companies demanding that she fork over her patients' medical records, the doctor has waged a paper war against insurers -- to no avail.

Any day now, Hunter expects to get the same kind of bill that many of her colleagues have found in the mail -- demands for $30,000, $80,000, even $200,000 in reimbursements, payable immediately.

Since federal privacy rules were loosened last month, insurers now have the right to see your records without notice to you, enabling them to search for discrepancies in how doctors code your treatments. If the insurer demands 10 patient files and finds reason to bounce back three of those claims, the company then -- here's the astonishing part -- extrapolates from those 10 records to dun the doctor for 30 percent of all claims over several years.

"I'm a small-town doc with two kids, working by myself, and I'm not earning any six-figure income," Hunter says. "Docs like me go into these deals with insurance plans even though we can barely break even: I charge $74 for a Level 3 visit, a common cold, sore throat. The insurance company only pays me $35; I absorb the difference. Now on top of that, they're searching my records to find ways to take even that amount back.

"I like what I do, and now look what I have to spend my time doing. Insurance companies know that a small practice doctor like me can't hire a lawyer to defend our claims. I cut the grass, cook and clean, live in a modest neighborhood. I don't drive a Mercedes. I buy my clothes at thrift shops. And now I may have no choice but to close my practice."

Russell Libby, a Fairfax pediatrician and ex-president of the Fairfax County Medical Society, says a frightening number of doctors are retiring early or leaving the field because they can no longer make ends meet. The Fairfax society is joining physicians in 15 states in lawsuits against health plans that conduct these audits.

"The insurers don't say, 'You're in error, and here's how you can fix your ways,' " says Libby. "They don't care about the quality of your care. They're just looking in your notes for opportunities to recoup dollars as pure income for them. And it's all completely invisible to the patient."

One insurer, United Healthcare, says the drive to keep doctors accountable affects "only 2 percent of our physicians, and the letters are flagged by unusual billing patterns. The cost of medical care is outrageous, and you've got to watch the pennies," says United's Debora Spano.

But doctors say it's the insurers who are being subjective. One physician in Leesburg said Trigon insurance ordered her to turn over 10 of her patients' records, then scoured those records for cases in which she had, for example, billed for a moderate-level office visit when the insurer said a low-level visit would suffice. Then she got a demand for $170,000.

The doctor, who declined to be named because she said Trigon required her to sign a confidentiality agreement when she settled with it, was so traumatized that she has dropped most of her insurance plans.

This doctor knew she had not overbilled; rather, she underreported the time she devotes to patients. So she fought: After more than a year's battle and $50,000 in legal fees, she settled with Trigon for $30,000.

Despite lowering her prices after she dropped the plans, she has lost about a third of her patients. "But the alternative was to push everyone out the door in three minutes, and that's not why I got into medicine," she says.

Insurers reject the notion that they're stopping doctors from providing optimal care. "That's a very subjective point, and we're looking at objective measures," Spano says.

Insurers are stepping up the pressure, says Fairfax obstetrician Robert Bettini. In the past year, he and his partners have seen insurers audit their records, delay payments by months and disburse different payments for identical procedures.

"We're reduced to going through the payments one by one, trying to get them to correct the fees," says Bettini, whose office has two full-time workers handling paperwork for five doctors.

The change is all for the bad, doctors say. "Thirty years ago, when I started," Bettini says, "we had one ledger sheet, we wrote down your $14 office visit, you got a paper receipt and everybody was happy."