NEW YORK (MONEY Magazine) - Consider, just for a moment, the swirl of the modern health-care system. One wrong keystroke by a hospital administrator can land you in red tape hell.

That's enraging -- and scary.

"Would you believe a thousand-dollar toothbrush?" says Nora Johnson, a medical-billing auditor who has seen that and a lot of other absurdities. "More than 90 percent of the bills I review are either wrong or padded beyond belief."

Her own husband was once charged for blood tests for a newborn as part of his hip-replacement surgery. ("I was pretty sure he hadn't had a baby.")

If billing errors result in overcharging or, worse, a denied claim, understanding the bureaucracy -- the very thing that drives you nuts -- is your best offense.

How to fight back:

Your bill will be awash with medical shorthand for the treatment you received. There are two kinds of codes:

• Diagnostic codes (a.k.a. ICD-9 codes), which identify what was wrong with you
• Procedure codes (a.k.a. CPT codes), which describe what treatment you received

Coding problems can be the result of either blatant padding (one procedure to remove tonsils and adenoids is "unbundled" and billed as two separate procedures) or keystroke errors (one typo causes a mismatch between the ICD-9 and the CPT codes, and your claim is branded a "coding error" and rejected). If your claim bounces back or the bill seems high, ask the hospital or doctor for a thorough explanation of each and every code.

Everyone knows you're supposed to hang on to bills, but here's something most people miss: doctor's orders. Every time your physician prescribes something -- blood tests, X-rays, medication -- it's recorded in her standing orders.

You have a right to this stuff, so request a copy from the billing office. Keep it in a personal medical file, which should also include the following documents:

• Reports by any technician handling a procedure, as well as the nurses who administer medication or shuttle you around in your paper gown
• Itemized bills (request these from your doctors or hospital, possibly after your treatment visit)
• Your insurance paperwork
• Your own notes from each doctor visit

Send (certified) a detailed letter to your doctor's office or hospital requesting a corrected bill. Then send (certified) another, equally detailed letter describing the problem, including your documentation, to the insurer. Don't forget copies of the doctor's orders and the bill.

If the doctor did order a test or procedure but the orders weren't carried out, you'll need documentation proving that. (Paperwork, as you may have surmised, is pretty much your lifeblood here.) Most insurers have a time limit, typically 30 or 60 days, within which they'll consider routine appeals. So get a move on.

Next: Fees, fees and more fees