A shakeup in managed health care may not have to wait for whomever occupies the White House next year.

Just as his predecessor forced changes on Wall Street, Andrew Cuomo, the New York State attorney general, has begun a very ambitious investigation that could change the way health insurance does business. Cuomo says that his office is examining a "scheme by health insurers to defraud consumers by manipulating reimbursement rates."

At issue is how the insurers compute "reasonable and customary" rates to health-care providers that are outside the insurer's network. Cuomo contends that providers are not realistically reimbursed and that patients are then forced to pay the difference.

Cuomo is focusing on Ingenix, a unit of UnitedHealth Group, which operates a database that most major health insurers use to set reimbursement rates.

"When insurers like United create convoluted and dishonest systems for determining the rate of reimbursement, real people get stuck with excessive bills and are less likely to seek the care they need," Cuomo said in a statement.

His office is threatening to sue UnitedHealth. It has also sent 16 subpoenas to insurers, including Aetna and Cigna.

How rates and costs are determined and how they are disclosed are at the heart of the frustrations patients and physicians have with health insurance.

"In an era of increasing health-care transparency, it is shocking and unacceptable for a health insurer to profit from deliberately withholding information from patients and physicians," Dr. Nancy Nielsen, president-elect of the American Medical Association, said about the New York investigation.

The UnitedHealth unit Ingenix is the largest provider of health-care billing information in the country. It had revenue of more than $1.7 billion last year, a 46 percent increase from 2006.

UnitedHealth says it is cooperating with the investigation.