PHOENIX -- Medical records contain some of the most private and personal information of someone's life, but authorities say there is a lucrative black market for them.

Arizona Attorney General Terry Goddard said his office has seen an increase in complaints, usually involving companies that bill Medicare for procedures that never took place.

"There is a lively market in medical IDs," Goddard said.

Last March, Valley resident Aaron Cohn received a bill in the mail for a pancreatic cyst removal. One problem: Cohn never had that surgery.

Based on the information he had, it appeared that someone underwent a medical operation using Cohn's insurance and identification.

In a similar case, Stanley Gorodenski said he received a bill for some medical equipment he never ordered and never received.

Nevertheless, the billing company demanded his Medicare account.

Medical identity theft is not just a financial crime, some groups say.

It can lead to a loss of insurance coverage, and to hospitals and doctors having records with the wrong blood type specified, allergies or drug information under a person's name.

"You never know how it's going to affect your coverage or how they treat you if you do … have an emergency where you're trucked into the hospital," Cohn said. "God forbid (you're) unconscious or can't talk for yourself."

The hospital billing company that sent Cohn's bill investigated the incident.

"In this certain case, it was human error, and nothing much more than human error," Scottsdale Healthcare spokeswoman Alice Giedraitis said. "With one simple keystroke, this patient was billed incorrectly."

She said the hospital took care of the bill as soon as it learned of the problem; however, experts said the best practices are to stay on top of medical records and open all medical bills immediately.

"The bottom line is you need to verify that someone in your family had that procedure," Goddard said.

Experts said there are other ways people can protect themselves:

• Look at every benefits statement received in mail from the insurance company
• Report any lost or stolen insurance cards immediately.
• Check credit reports regularly

Additionally, avoid any "out of the blue" medical screening offers. There are documented cases where the "health screenings" were set up just to steal medical identities.