Congressional investigators have discovered that large health insurers in every region of the country are relying on faulty databases to underpay millions of valid insurance claims.

    In a report released Wednesday, the Senate Commerce Committee said insurance companies nationwide have failed to provide consumers with accurate or understandable information about how they calculate "reasonable" or "customary" charges for out-of-network care.

    Insurers also signed contracts prohibiting them from disclosing information about the databases to consumers or doctors, the report said.

    The flawed databases are owned by Ingenix Inc., a subsidiary of UnitedHealth Group Inc. UnitedHealth recently settled with the New York attorney general's office to resolve charges that Ingenix drew up billing rates that underpaid hospitals and doctors for out-of-network care.

    Patients had to make up the difference. It is unclear how much they have overpaid over the years.

    An Ingenix spokeswoman said the company stands by the integrity of its databases. The two databases in question by the committee represent less than 2% of Ingenix's overall business. Ingenix also said it doesn't set actual rates for health procedures.

    Other insurers that purchased Ingenix data in New York - Aetna Inc., CIGNA Corp., and Wellpoint Inc. among them - also paid into the settlement. Under that agreement, the insurers will help pay for and then use a new not-for-profit research entity that will help determine prices for out-of-network care.

    Commerce Committee Chairman John Rockefeller, D-W.Va., launched the committee investigation in March, in the wake of the UnitedHealth settlement.

    Committee oversight staffers sought data from 18 large insurers that didn't participate in the New York settlement, including American International Group Inc., Humana Group Inc., the Kaiser Foundation Group, several Blue Cross Blue Shield units, and UnumProvident Corp.

    Together with the New York investigation, the committee's findings represent roughly two-thirds of the health-insurance market.

    The Ingenix databases represent "the great black box of the health-care industry," according to one health-care CEO quoted in the report. Ingenix also is the only commercial source of such data.

    Providers and patients have suspected for years that insurers were underpaying for out-of-network care, but they haven't been able to prove it.

    Committee investigators found that Ingenix developed its payment models based on claims data provided by its customers, the insurance companies.

    A committee aide said those companies sometimes would "scrub" the data sent to Ingenix - throwing out outlying high costs. Ingenix then would use questionable statistical models to come to its own rate estimates.

    The committee's report comes at a critical moment in Congress, as lawmakers are struggling to craft a massive overhaul to the health-care system designed to cover some 45 million uninsured Americans.

    In addition to chairing the Commerce Committee, Sen. Rockefeller also chairs the health subcommittee of the Finance Committee, one of two key Senate panels negotiating the health-care bill.

    He hopes to insert into the health-care bill language creating some type of independent evaluator that can certify that health claims are evaluated properly.

    In the meantime, Commerce Committee investigators likely will continue to drill down into individual companies' practices to understand how they arrive at certain claims rates. The committee also could look into smaller regional insurance carriers to see if they, too, are using faulty data.

    Republicans and other champions of private-sector insurers have long argued that making health care more consumer-friendly would drive down costs because patients could "shop around" for the best care.

    But Sen. Rockefeller and other health-policy experts argue that the lack of information in the private health-insurance market has made competition and informed consumer choice almost impossible.