From ICD10 to ORPHAcodes: paving the way towards improved identification systems for rare diseases

Abstract Background The International Classification of Diseases 10th revision (ICD10) and its clinical modification (ICD10CM) are commonly used for the identification of diseases occurrence worldwide. In Spain, diagnoses are coded with its Spanish version (ICD10ES) since 2016 regardless of the prevalence of diseases. Rare diseases (RDs) are scrambled among common diseases in ICD10 and its derivatives and many RDs dońt have a specific ICD10 code, delaying a proper identification. Orphanet developed a classification system specific for RDs called ORPHAcode. This study aims to characterize whether ICD10ES mapping to ORPHAcodes improves RDs identification and which kind of disorders would benefit the most. Methods 95% of the disorder level ORPHAcodes indexed at Orphanet was mapped to codes from 20 ICD10ES chapters by comparing the descriptors associated in both classifications. ORPHAcodes were then clustered based on their assigned ICD10ES chapter and the redundancy of each individual ICD10ES code was calculated by counting the ORPHAcodes they mapped to. 3 groups were established: Group 1 (1 ORPHAcode per ICD10ES), Group 2 (between 2-49 ORPHAcodes per ICD10ES) and Group 3 (≥50 ORPHAcodes per ICD10ES). Results 5588 ORPHAcodes were correlated to 1677 ICD10ES codes. 1051 were group 1, 3261 group 2 (615 ICD10ES) and 1276 group 3 (11 ICD10ES). Most of the Orphacodes correlated to “Q” (>40%), “G” (>14%) and “E” (>12%) chapters of ICD10ES. Regarding specificity, “G” and “Q” were also the only chapters including group 3 ORPHAcodes, while less than 10% of the ORPHAcodes linked to these chapters were in group 1. Conclusions New and improved ICD10ES codes are required because just 20% of all ORPHAcodes studied were into group 1. Especial care should be put on the two majoritarian chapters, “Q:Congenital Anomalies” and “G:Nervous System”, that show the lowest specificity for RDs. Complementary use of ORPHAcodes would improve the identification and registry of RDs either. Funded: Project RD-CODE Key messages The lack of a specific chapter for Rare Diseases in the InternationaI Classification of Diseases hinders their identification and therefore their study. Direct mapping between ICD10 and ORPHAcodes or the use of ORPHAcodes for diagnoses codification of Rare Diseases would enable better detection and epidemiological analysis.