ICD-10-CM Crosswalks in the primary care setting: Assessing reliability of the GEMs and reimbursement mappings

Objective The general equivalence mappings (GEM_s) and reimbursement mappings (RM_s) facilitate translation between ICD-9-CM and ICD-10-CM. This study compared prospectively dual-encoded diagnoses assigned by professional coders with the GEMs/RM_s in a clinical setting. Materials and Methods Professional coders manually encoded diagnoses from 100 primary care notes into both ICD- 9-CM and ICD-10-CM. The investigators evaluated whether manual mappings were reproducible using the GEM_s/RM_s. Reproducible mappings with one ICD-9-CM and one ICD-10-CM code ("one-to-one") were classified as exact or approximate using GEMs flags. Mismatches were characterized manually. Results Manual encodings were reproducible from the forward GEM_s, backward GEM_s, and RM_s in 85.2%, 90.4%, and 88.1% of diagnoses, respectively. For one-to-one, reproducible mappings, 61% (forward) and 63% (backward) were approximate mappings compared to 85% and 95% in the GEM_s as a whole. Mismatches between manual and GEMs encodings were due to differences in coder interpretation (11%-13%), subtle hierarchical differences (52%-55%), or unknown reasons (32%-35%). Discussion This study highlights inconsistencies between manual encoding and using the GEM_s/RM_s. The number of approximate mappings in our population compared to all one-to-one GEMs entries supports the notion that statistics describing the GEM_s as a whole might not represent the most important mappings for each organization. The mismatch characteristics highlight the subtle differences between manual encoding and using the GEM_s/RM_s. Conclusion These results support the need for organizations to assess the GEMs and RMs in their own environment to avoid changes in reimbursement and longitudinal statistics.