The OIG has issued a report on "Invalid Prescriber Identifiers on Medicare Part D Drug Claims." Prescriber identifiers on Medicare Part D drug claims are intended to indicate that legitimate practitioners have prescribed medications for Medicare enrollees. In a review of 2007 Part D claims, the OIG concluded that more than 18 million claims representing more than $1.2 billion contained invalid prescriber identifiers (e.g., identifiers were not listed as valid identifiers in the National Provider Identifier, DEA number, or Unique Physician Identification Number registry databases, or they were deactivated or retired). The OIG recommended procedures to improve detection of invalid prescriber identifiers.