Dementia Identification with EMR

The major data sources for identification of dementia cases in the UK comprise EMR hospitalisation data, death records and dispensed prescribing records. From these sources, we categorise any dementia into the following clinicopathological subtypes: Alzheimer's dementia, Vascular dementia, Other dementia (any dementia type other than Alzheimer's or Vascular), Unspecified dementia (where a specific sub-type is not recorded) and Possible dementia (where the diagnosis is not clear for it to definitively be dementia). For individuals with dementia, the earliest date of mention of dementia (in any of the sources) is taken as a surrogate for the incident date of dementia.

For more information about the phenotype, please refer to linked publications.

We use a combination of ICD-10 codes (for hospitalisation and death records) and BNF codes (prescribing records) to adjudicate dementia sub-type as listed in the concept list below. With regards to prescriptions, given that in the UK, medications for dementia (donepezil hydrochloride, galantamine, rivastigmine, and memantine hydrochloride) are largely indicated for individuals with Alzheimer dementia, a history of redeeming a prescription for one of these drugs can be considered indicative of a diagnosis of Alzheimer's.

Given the longitudinal nature of our records, we make use of the entire patient history to determine a distribution over dementia sub-types (if any). Specifically, we summarise each patient's coding episode into a binary indication of whether each dementia subtype (Alzheimer's, Vascular, Other, Unspecified or Possible) is mentioned or not. For each patient, we then count the number of coding episodes for each subtype and divide it by the total number of coding episodes over all subtypes, to yield a proportion (probability) over dementia subtypes for that patient - if the patient has no evidence of dementia, then this proportion is taken to be all 0s. Subsequently, for dementia subjects, the earliest date of mention of dementia (in any of the sources) is taken as a surrogate for the incident date of dementia, while the last date on record for a non-dementia patient is taken to be the last date of follow-up for that subject.

For more detail on implementation, please refer to linked publications.