A unidirectional mapping of ICD-8 to ICD-10 codes, for harmonized longitudinal analysis of diseases

Mette Krogh Pedersen, Robert Eriksson, Roc Reguant, Catherine Collin, Helle Krogh Pedersen, Freja Karuna Hemmingsen Sørup, Christian Simon, Anna Marie Birch, Michael Larsen, Anna Pors Nielsen, Kirstine Belling, Søren Brunak*

*Corresponding author af dette arbejde
2 Citationer (Scopus)


Periodic revisions of the international classification of diseases (ICD) ensure that the classification reflects new practices and knowledge; however, this complicates retrospective research as diagnoses are coded in different versions. For longitudinal disease trajectory studies, a crosswalk is an essential tool and a comprehensive mapping between ICD-8 and ICD-10 has until now been lacking. In this study, we map all ICD-8 morbidity codes to ICD-10 in the expanded Danish ICD version. We mapped ICD-8 codes to ICD-10, using a many-to-one system inspired by general equivalence mappings such that each ICD-8 code maps to a single ICD-10 code. Each ICD-8 code was manually and unidirectionally mapped to a single ICD-10 code based on medical setting and context. Each match was assigned a score (1 of 4 levels) reflecting the quality of the match and, if applicable, a "flag" signalling choices made in the mapping. We provide the first complete mapping of the 8596 ICD-8 morbidity codes to ICD-10 codes. All Danish ICD-8 codes representing diseases were mapped and 5106 (59.4%) achieved the highest consistency score. Only 334 (3.9%) of the ICD-8 codes received the lowest mapping consistency score. The mapping provides a scaffold for translation of ICD-8 to ICD-10, which enable longitudinal disease studies back to and 1969 in Denmark and to 1965 internationally with further adaption.

TidsskriftEuropean Journal of Epidemiology
Udgave nummer10
Sider (fra-til)1043-1052
Antal sider10
StatusUdgivet - okt. 2023


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