Many families with medical insurance are shocked when an illness or accident strikes and their insurer leaves them with tens of thousands of dollars in unpaid bills.

In most cases, that's because they're underinsured. Their policies have such strict limits on how much the insurer will pay, they're left holding the bag on most of the costs.

But insurers also reject 10% to 15% of what appears to be legitimate claims.

Insurance companies actually have computer programs called "denial engines" that review every claim, looking for reasons to turn it down.

In some instances, those rejections are based on technicalities, such as failing to obtain the insurer's permission before a procedure or filing the claim too late to qualify for reimbursement.

In other cases, insurers deny claims because the care is deemed to be unneeded or experimental.

These kinds of arbitrary decisions must be challenged through the insurer's in-house appeals process -- a potentially lengthy and pretty much secret process that usually upholds the insurer's original denial.

But in 43 states and the District of Columbia, policyholders can appeal that final denial through state insurance commissions.

Patients win about half of those appeals, and if these state regulators say an expense should be covered, then it's covered.

These commissions are not consumer advocates. They're regulators, and if you lie about your claim or dispute, they'll come after you for insurance fraud.

But they all offer advice and information. If you need help or think your insurance company is trying to rip you off, this should be one of the first places you turn.

The National Association of Insurance Commissioners has a Web site called InsureU that offers buckets of insurance information.

It can help explain options and plans, and get you familiar with industry lingo before filing a complaint.

That association also allows you to file a complaint about an insurer with your state commission.