title: Assessing and Measuring Chronic Multimorbidity in the Older Population: A Proposal for Its Operationalization.
abstract: BACKGROUND
  Although the definition of multimorbidity as "the simultaneous presence of two or more chronic diseases" is well established, its operationalization is not yet agreed. This study aims to provide a clinically driven comprehensive list of chronic conditions to be included when measuring multimorbidity.
  
  
  METHODS
  Based on a consensus definition of chronic disease, all four-digit level codes from the International Classification of Diseases, 10th revision (ICD-10) were classified as chronic or not by an international and multidisciplinary team. Chronic ICD-10 codes were subsequently grouped into broader categories according to clinical criteria. Last, we showed proof of concept by applying the classification to older adults from the Swedish National study of Aging and Care in Kungsholmen (SNAC-K) using also inpatient data from the Swedish National Patient Register.
  
  
  RESULTS
  A disease or condition was considered to be chronic if it had a prolonged duration and either (a) left residual disability or worsening quality of life or (b) required a long period of care, treatment, or rehabilitation. After applying this definition in relation to populations of older adults, 918 chronic ICD-10 codes were identified and grouped into 60 chronic disease categories. In SNAC-K, 88.6% had ≥2 of these 60 disease categories, 73.2% had ≥3, and 55.8% had ≥4.
  
  
  CONCLUSIONS
  This operational measure of multimorbidity, which can be implemented using either or both clinical and administrative data, may facilitate its monitoring and international comparison. Once validated, it may enable the advancement and evolution of conceptual and theoretical aspects of multimorbidity that will eventually lead to better care.
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.|EpiChron Research Group on Chronic Diseases, Aragon Health Sciences Institute (IACS), IIS Aragon, REDISSEC-ISCIII, Spain.
authors.forename: Amaia
authors.initials: A
authors.lastname: Calderón-Larrañaga
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.|Department of Geriatrics, Neurosciences and Orthopedics, Catholic University of Rome, Italy.
authors.forename: Davide L
authors.initials: DL
authors.lastname: Vetrano
authors.affiliation: Department of Geriatrics, Neurosciences and Orthopedics, Catholic University of Rome, Italy.
authors.forename: Graziano
authors.initials: G
authors.lastname: Onder
authors.affiliation: EpiChron Research Group on Chronic Diseases, Aragon Health Sciences Institute (IACS), IIS Aragon, REDISSEC-ISCIII, Spain.|San Pablo Health Centre, Aragon Healthcare Service (SALUD), Spain.
authors.forename: Luis A
authors.initials: LA
authors.lastname: Gimeno-Feliu
authors.affiliation: EpiChron Research Group on Chronic Diseases, Aragon Health Sciences Institute (IACS), IIS Aragon, REDISSEC-ISCIII, Spain.|San Pablo Health Centre, Aragon Healthcare Service (SALUD), Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Coscollar-Santaliestra
authors.affiliation: Department of Geriatrics, Neurosciences and Orthopedics, Catholic University of Rome, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Carfí
authors.affiliation: Department of Geriatrics, Neurosciences and Orthopedics, Catholic University of Rome, Italy.
authors.forename: Maria S
authors.initials: MS
authors.lastname: Pisciotta
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Angleman
authors.affiliation: Department of Geriatric Medicine, Radboud Alzheimer Center, Radboud Institute for Health Sciences, Radboud University Medical Centre, The Netherlands.
authors.forename: René J F
authors.initials: RJF
authors.lastname: Melis
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.
authors.forename: Giola
authors.initials: G
authors.lastname: Santoni
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.
authors.forename: Francesca
authors.initials: F
authors.lastname: Mangialasche
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.
authors.forename: Debora
authors.initials: D
authors.lastname: Rizzuto
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.
authors.forename: Anna-Karin
authors.initials: AK
authors.lastname: Welmer
authors.affiliation: Department of Geriatrics, Neurosciences and Orthopedics, Catholic University of Rome, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bernabei
authors.affiliation: EpiChron Research Group on Chronic Diseases, Aragon Health Sciences Institute (IACS), IIS Aragon, REDISSEC-ISCIII, Spain.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Prados-Torres
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.|Department of Clinical and Experimental Sciences, University of Brescia, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Marengoni
authors.affiliation: Aging Research Center, NVS Department, Karolinska Institutet, Stockholm University, Sweden.|Stockholm Gerontology Research Center, Sweden.
authors.forename: Laura
authors.initials: L
authors.lastname: Fratiglioni
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002908:Chronic Disease / Q000145:classification* / Q000453:epidemiology*; D015897:Comorbidity / Q000639:trends*; D005260:Female; D006801:Humans; D038801:International Classification of Diseases; D008297:Male; D008875:Middle Aged; D013548:Sweden
keywords: Chronic disease; Epidemiology; International Classification of Diseases