Prevalence and outcomes of recorded dementia vary by data source: a population cohort study of 133,407 older adults

Abstract Background Dementia diagnoses are captured across multiple routine data sources, but discrepancies between these may affect care and research. This study determined the prevalence and overlap of recorded dementia across primary care, hospital, and community prescribing data sources in a UK regional cohort, and examined whether outcomes differed by the setting in which dementia was first recorded. Methods Retrospective cohort study of adults ≥65 years (n=133,407) in a large Scottish health board. Dementia diagnoses recorded from 01/04/2016 to 01/04/2020 were identified across linked primary care, hospital discharge, and prescribing records. Associations between source of first recorded dementia diagnosis and subsequent mortality and emergency hospitalisation were estimated using Cox proportional hazards and Fine–Gray competing risks models. Results At baseline (01/04/2016), 7544/133407 individuals (5.7%) had recorded dementia: 95.1% in primary care, 73.3% in hospital, and 54.3% in prescribing records. Over four years, 7359 of the remaining 125,863 individuals (5.8%) had newly recorded dementia: 70.2% in primary care, 22.2% in hospital, and 7.6% in prescribing records. Only 35.9% of hospital-recorded diagnoses were coded in primary care records within a year. People first diagnosed in hospital were older, more frail, more socioeconomically deprived, and had higher mortality than those first diagnosed in primary care (365days: aHR 1.29, 95%CI 1.19-1.41). Conclusions Dementia is variably recorded across routine datasets, and the setting in which dementia is first recorded identifies groups with markedly different prognosis. Improved data source integration and scrutiny of hospital-based diagnostic pathways are needed to ensure diagnoses are reliably transferred and people with dementia receive timely, equitable post-diagnostic care.