Catalog of 199 register-based definitions of chronic conditions

Abstract

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.

A Nationwide Study of Prevalence Rates and Characteristics of 199 Chronic Conditions in Denmark

“…A thorough description of the distinct phases and methods used are provided elsewhere [44][45][46]. In short, a 'chronic condition' was defined in line with previous studies, i.e.…”

“…the 'condition had lasted or was expected to last twelve or more months and resulted in functional limitations and/or the need for functional limitations and/or the need for ongoing medical care' [47][48][49]. An expert panel consisting of professors, medical specialists and other experts from Aalborg University, the Clinical Institute of Aalborg University at Aalborg University Hospital, the Department of Clinical Epidemiology at Aarhus University Hospital, and others was consulted using the Delphi method in order to identify which of the approximately 22,000 ICD-10 codes and conditions could be considered 'chronic' based on the definition [44]. The ICD-10 codes were aggregated to 199 conditions, yet several conditions included subgroups of ICD-10 codes; thus, some consequently contained multiple conditions within the same disease area.…”

“…Since many chronic conditions last longer than the defined 12 months, but do not last for a lifetime, the varying 'chronicity' of conditions was divided into four groups of severity [44]:…”

“…The same applied to GP services indicating, for example, diabetes or chronic obstructive lung disease (COPD) treatment, etc., where no hospital diagnosis was found. The details of all 199 unique definitions, their categorisation into one of the four categories and algorithms for replication can be found elsewhere [44,45].…”

“…All registers had a unique civil registration number for each person; furthermore, birth date, gender and other information were derived from the Danish Civil Registration System [43]. The registers used are described in more detail in other studies [44,45]. Table 1 summarises the details of the registers used.…”