NEW ORLEANS (AP) — A New York doctor has admitted to billing the federal government for unnecessary medical tests that were not performed on patients.

The U.S. Attorney's Office in New Orleans said Dr. Yelena Ivanova pleaded guilty Friday before U.S. District Court Judge Lance Africk to conspiracy to commit health care fraud.

Officials say the patients received narcotics for their cooperation.

Ivanova, of Brooklyn, N.Y., is the third doctor to plead guilty in the case, which centered on their conduct at health clinics in Metairie and Kenner.

Federal investigators say the clinics bilked the government out of $21 million.

Like the other two doctors who pleaded guilty, Ivanova could serve as many as 10 years in prison for her involvement in the scheme.