PURPOSE: An increasing proportion of older adults accessing hospital care are living with multimorbidity, with a high degree of complexity of multimorbidity in older hospital populations expected. We aimed to assess approaches taken to characterise multimorbidity in older adults accessing hospital care, including how complexity is considered. METHODS: Following established scoping review guidelines, all published studies that characterised multimorbidity in a hospital population, with average age ≥ 65 years, were identified via a prespecified search strategy. Six electronic databases were searched to identify peer-reviewed literature published to September 2023 meeting eligibility criteria. Screening was undertaken by two independent reviewers, and data extracted using a standard proforma. RESULTS: Of 5305 titles and abstracts screened, 75 papers, reporting on 72 unique study populations across 24 countries, met inclusion criteria. There was heterogeneity in most aspects of characterisation. Multimorbidity was defined in 43% (n = 31/72) of studies
most (n = 59/72, 82%) aimed to describe a multimorbidity-outcome association. Number of conditions considered ranged from 2 to 285 and weighted indices were used as a measure of multimorbidity in 75% (n = 54/72) of studies, with 56% (n = 40/72) using a version of the Charlson Comorbidity Index. Complexity was explicitly studied in 17% (n = 12/72) of studies. DISCUSSION: Our review highlights heterogeneity in characterisation of multimorbidity in older adults accessing hospital care, with limited consideration of complexity. As the proportion of older adults accessing hospital care who are living with multimorbidity increases, better characterisation of their multiple conditions and associated complexity is a priority to ensure delivery of appropriately tailored care.