ABSTRACT
Objective-On October 1, 2015, the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) replaced ICD-9-CM (Ninth Revision) as the diagnosis coding scheme for the U.S. health care system. This study evaluates the impact of this change on the way the National Center for Health Statistics (NCHS) reports diagnosis data for the National Ambulatory Medical Care Survey (NAMCS). Methods-The patient visit records of office-based physicians from the 2014 NAMCS final quarter (n = 20,942) were reviewed. The diagnoses assigned to each record were coded in both ICD-9-CM and ICD-10-CM by professional medical coders. NCHS staff reviewed how well the codes of the primary diagnosis under the two coding systems corresponded to each other. Results-The review showed that 89% of the visit records had compatible ICD-9-CM and ICD-10-CM codes for the primary diagnosis, meaning that the primary diagnosis would be grouped under the same Primary Diagnosis Group (PDG) according to both ICD-9-CM and ICD-10-CM, and it would be correctly assigned to only one PDG. The reasons for mismatches in the ICD-10-CM assignments included coder error (5%), documentation issues such as uncodable diagnoses (3%), and differences between ICD-9-CM and ICD-10-CM (2%).
