Claims for all services and hospital inpatient procedures provided on or after the compliance deadline must use ICD-10 diagnosis and inpatient procedure codes. (This does not apply to CPT coding for outpatient procedures.) Claims that do not use ICD-10 diagnosis and inpatient procedure codes cannot be processed. It is important to note, however, that claims for services and inpatient procedures provided before the compliance date must use ICD-9 codes.
Source: Centers for Medicare & Medicaid Services, www.cms.gov, February 2014.