ICD-11 extension codes support detailed clinical abstraction and comprehensive classification

BACKGROUND: The new International Classification of Diseases—11th revision (ICD-11) succeeds ICD-10. In the three decades since ICD-10 was released, demands for detailed information on the clinical history of a morbid patient have increased. METHODS: ICD-11 has now implemented an addendum chapter X called “Extension Codes”. This chapter contains numerous codes containing information on concepts including disease stage, severity, histopathology, medicaments, and anatomical details. When linked to a stem code representing a clinical state, the extension codes add significant detail and allow for multidimensional coding. RESULTS: This paper discusses the purposes and uses of extension codes and presents three examples of how extension codes can be used in coding clinical detail. CONCLUSION: ICD-11 with its extension codes implemented has the potential to improve precision and evidence based health care worldwide.