A pitfall of using general equivalence mappings to estimate national trends of surgical utilization for pediatric patients

Background: General equivalence mappings (GEMs) were developed to facilitate a transition from International Classification of Diseases, Ninth Revision (ICD-9) to ICD, Tenth Revision (ICD-10). Validation of GEMs is suggested as coding errors have been reported for adult populations. The purpose of this study was to illustrate limitations of the GEMs for pediatric surgical procedures. Methods: Using the 2014 to 2016 National Inpatient Sample, we evaluated all patients undergoing inguinal hernia repair. ICD-9 codes for the repair were independently classified as laparoscopic or open approach by two surgeons. Conversions of the ICD-9 to ICD-10 codes were compared between the GEMs strategy and surgeons' manual mapping. National trends were compared for overall, adult, and pediatric populations. Results: We found significant inconsistencies in the proportion of laparoscopic inguinal hernia repair based on mapping strategies employed. For adults, the comparison of the proportions in 2016 was 17.79% (GEMs) versus 21.44% (Manual). In pediatric population, the contrast was 0.45% (GEMs) versus 17.75% (Manual), and no laparoscopic repair cases were found using GEMs in the last quarter of 2015. Conclusion: Some conversions of ICD-9 and ICD-10 using the current GEMs are not valid for certain populations and procedures. Clinical validation of coding conversions is essential. Level of evidence: Level V.