Catalog of 199 register-based definitions of chronic conditions

Introduction: The aim of the current study was to present and discuss a broad range of register-based definitions of chronic conditions for use in register research, as well as the challenges and pitfalls when defining chronic conditions by the use of registers. Materials and methods: The definitions were defined based on information from nationwide Danish public healthcare registers. Medical and epidemiological specialists identified and grouped relevant diagnosis codes that covered chronic conditions, using the International Classification System version 10 (ICD-10). Where relevant, prescription and other healthcare data were also used to define the chronic conditions. Results: We identified 199 chronic conditions and subgroups, which were divided into four groups according to a medical judgment of the expected duration of the conditions, as follows. Category I: Stationary to progressive conditions (maximum register inclusion time of diagnosis since the start of the register in 1994). Category II: Stationary to diminishing conditions (10 years of register inclusion after time of diagnosis). Category III: Diminishing conditions (5 years of register inclusion after time of diagnosis). Category IV: Borderline conditions (2 years of register inclusion time following diagnosis). The conditions were primarily defined using hospital discharge diagnoses; however, for 35 conditions, including common conditions such as diabetes, chronic obstructive lung disease and allergy, more complex definitions were proposed based on record linkage between multiple registers, including registers of prescribed drugs and use of general practitioners’ services. Conclusions: This study provided a catalog of register-based definitions for chronic conditions for use in healthcare planning and research, which is, to the authors’ knowledge, the largest currently compiled in a single study.