Health insurer Humana faces multiple federal investigations over allegations it overbilled the government.

The company, which insures more than 2 million Americans and has a yearly revenue of around $36 billion, may have overbilled the government when treating elderly patients enrolled in its Medicare Advantage plan, court records reveal.

While the status of the investigations is not clear, they involve several branches of the U.S. Department of Justice, according to a recent report by the Center for Public Integrity.

The U.S. Attorney's Office in Miami wrote in a March court document that at least one of the probes would be completed and made public within the “next few months.”

A similar criminal case involving overbilling allegations has been opened at the U.S. Attorney’s Office in West Palm Beach, Fla., as well, Public Integrity revealed.

The Miami case, which was filed in September 2010 and unsealed in early May, alleges a South Florida doctor inflated billings for two dozen or more Humana patients. The whistleblower added new allegations to the lawsuit two weeks ago.

“We continue to investigate these matters ourselves and to cooperate with the Department of Justice, as we have all along,” Humana spokesman Tom Noland said in a recent email.

Noland also noted that Humana “to our knowledge is not the subject of any criminal investigation.”

Consequences of these legal cases could be far-reaching for privately run Medicare Advantage plans, Public Integrity said.

These plans, which provide extra benefits for seniors and often cost less than standard Medicare, treat almost 16 million Americans and are expected to cost $150 billion this year.

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