(MONEY Magazine) – By now you know that if you're denied credit or slapped with a less-than-competitive rate on a loan, you should check your credit report for inaccuracies. But here's a trickier question: What do you do when you're hit with high insurance premiums or denied coverage altogether? Answer: Check your medical records for inaccuracies. Just as your credit report is a basis for lending decisions, your medical records are an important source for life and health insurers as they price and issue policies. Here too, errors can cost you. One mistyped diagnosis code can drive up premiums. If you're tagged as "rated" (read: riskier) vs. "preferred," you might pay $9,000 more for a $500,000, 20-year term life policy over the coverage period. The cure, says patients' rights advocate Marie Savard, M.D.: Get your records, and make sure that they have your health story straight.

Know What They Know

Privacy laws generally protect your medical records--created anytime you're treated by a health professional--from being seen by anyone without your consent. When you apply for an individual life, health or disability policy, though, you're asked to sign a release allowing the carrier to review those records. You can refuse, but then you won't get coverage.

Instead, see for yourself what's in your files. By law you have the right to view them, although you may need to pay for copying. Write to all the doctors' offices, hospitals and pharmacies you've visited in the past seven years, which is usually how long records must be kept. Say, "Please send me test results and discharge summaries for all appointments since 1999."

If you've ever applied for individual insurance, you'll also want to check with the Medical Information Bureau (MIB), a nonprofit that protects insurers from fraud by collecting red flags found during previous underwriting decisions. You can get one free report a year at mib.com.

Check for Mistakes

Once you've collected your paperwork, read through it carefully, watching for:

• A CONDITION YOU'VE NEVER HAD Maybe a nurse misread the doctor's scrawlings. Or perhaps a processor typed the wrong code (the medical community uses a system of numbers to denote diagnoses and treatments). Either way, one typo can turn a benign cyst (code 685) into chronic kidney failure (code 585).

• A DIAGNOSIS THAT'S MORE SERIOUS THAN YOU RECALL While heartburn may not pique the interest of potential insurers, the more severe Barrett's esophagus could. Whether such a misdiagnosis represents an honest mistake or a doc trying to boost his reimbursement, it can be a black mark on your file.

• ANYTHING OUT OF DATE Look for health issues you've gotten under control (say, high cholesterol) or past risk-related lifestyle habits (like smoking). Updating your file to note that you've quit cigarettes could help change your life insurance classification and save you $1,800 a year.

Set the Record Straight

Not all mistakes will be obvious to the untrained eye. So if your records are particularly complicated or you're unsure whether something is wrong, consider hiring a claims-assistance professional ($30 to $160 an hour; go to claims.org for referrals) to review your medical history, check the codes and help you figure out if any inaccuracies are fouling up your file. This person can also advocate on your behalf to get them fixed.

Or take the DIY approach to cleaning your files: Send certified letters, return receipt requested, to the practice of each doctor holding information you need to amend. Explain the mistake and offer any proof to the contrary that you have. The same procedure goes for making changes in your MIB file. If you don't get a satisfactory resolution with MIB, you can enter a "statement of dispute" on your record.

After you've corrected the errors, be sure to talk to your insurance agent, who may be able to help you nab lower premiums or reverse a denial of coverage.

Curtis Pesmen is the author of The Colon Cancer Survivors' Guide.

$48,100 How much more you might pay for a $500,000 term policy if a benign cyst is mistakenly coded as kidney failure

NOTE: Assumes a 20-year term policy and an otherwise healthy 35-year-old male.

SOURCE: Transamerica.