Background: The Lothian Birth Cohort 1936 (LBC1936) is a longitudinal study of ageing with well-characterised assessments, but until now, it has relied on self-report or proxies for dementia outcomes. This report describes a framework for clinical dementia ascertainment and its implementation. We report the prevalence of all-cause dementia and dementia subtypes in 865 individuals aged 70 years and older from the LBC1936. Methods: Electronic Health Records (EHR) of all participants were reviewed, and relevant information was extracted to form case vignettes for everyone with any record of cognitive dysfunction. The EHR data sources include hospital and clinic letters, general practitioner and hospital referrals, prescribed medications, imaging and laboratory results. Death certificate data were obtained separately. Clinician assessments were performed when there was concern about a participant's cognition. A diagnosis of probable dementia, possible dementia, or no dementia was agreed upon by a consensus diagnostic review board, comprised of a multidisciplinary team of clinical dementia experts who reviewed case vignettes and clinician assessment letters. For those with probable dementia, a subtype was also determined, where possible. Finally, we compared the agreement between our newly ascertained dementia outcomes with the existing self-reported dementia outcomes. Results: The EHR review identified 163 out of 865 (18.8%) individuals as having cognitive dysfunction. At the consensus diagnostic review board, 118/163 were diagnosed with probable all-cause dementia, a prevalence of 13.6%. Age-specific dementia prevalence increased with age from 0.8% (65-74.9 years) to 9.93% (85-89.9 years). Prevalence rates for women were higher in nearly all age groups. The most common subtype was dementia due to Alzheimer disease (49.2%), followed by mixed Alzheimer and cerebrovascular disease (17.0%), dementia of unknown or unspecified cause (16.1%), and dementia due to vascular disease (8.5%). Self-reported dementia outcomes were positive in only 17.8% of ascertained dementia outcomes. Conclusions: Dementia outcomes have been clinically ascertained in the LBC1936 using a robust systematic approach that closely aligns with diagnosing dementia in practice. This provides useful detailed outcomes for further analyses of LBC1936 to allow exploration of lifecourse predictors of dementia. Keywords: dementia; ascertainment; diagnosis; outcome; incidence; prevalence; ageing; older adults; longitudinal; electronic health record

The authors have declared no competing interest.

The present manuscript received no direct funding. All researchers are independent of their funders.

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