2012 ICD-9-CM Diagnosis Code 780.97. Altered mental status. ICD-9-CM 780.97 is a billable medical code that can be used to indicate a diagnosis on a reimbursement claim, however, 780.97 should only be used for claims with a date of service on or before September 30, 2015. For claims with a date of service on or after October 1, 2015, use an equivalent ICD-10-CM code (or codes).