Errors in medical bills can affect your credit rating long after you've recovered your health.

Take the case of Jean Mertz of Columbus, Miss.: She was turned down for new auto insurance last August and discovered the culprit was an anesthesiologist's bill from her gall-bladder surgery three years earlier.The medical-billing polygon that links consumers, medical providers, insurance companies, collection agencies and credit bureaus often leads to confusion and sometimes to credit-reporting errors that are difficult to untangle.

Many disputed entries on credit reports involve disagreement over who should pay an amount not covered by insurance. But it's also easy to get tripped up when one of the many bills sent out after a hospital stay goes astray.

In Mertz's case, the $468 anesthesiologist's bill was misaddressed and never reached her. After a collection agency contacted her by phone in 1992, her insurer paid in full.

Mertz says the collection agency assured her that her credit report would be cleared. So she was stunned to learn two years later that a collection account clouded her record.

Mertz says she eventually got the item removed from her credit history - but it took three months and dozens of phone calls.

The problem? To a collection agency, a bill that's turned over for collection is automatically delinquent, and a credit report reflects that even after the bill has been paid.

Mertz might have had the record corrected with less hassle, says Ted Smith of the American Collectors Association, by appealing directly to the anesthesiologist, who could have verified that the original billing address was incorrect and directed the collection agency to remove the item.

Other tips for avoiding medical-billing hassles:

- Do your best to keep track of who treats you during a hospital stay, and follow up to make sure that, between you and the insurance company, everyone gets paid.

- Don't expect to be off the hook for amounts not covered by insurance.