Predictors of costs of care in Alzheimer's disease: a multinational sample of 1222 patients.

BACKGROUND: The costs of care for patients with Alzheimer's disease are correlated with key measures of disease severity. This relationship is important in the economic evaluation of new treatments and is used to translate treatment efficacy into effects on costs through economic modeling. We aimed to identify what measures of disease severity are the most important predictors of societal costs of care and whether their relationship differs across countries.
METHODS: Interviews were conducted with 1222 patient and caregiver pairs residing in the community or in residential care settings in Spain, Sweden, United Kingdom, and the United States. Assessments included costs of care (Resource Utilization in Dementia) and key disease severity measures: cognitive function (Mini-Mental State Examination), ability to perform Activities of Daily Living (ADL-ability, Disability Assessment for Dementia [DAD]), and behavioral symptoms (Neuropsychiatry Inventory (NPI)-severity).
RESULTS: ADL-ability was the most important predictor of societal costs of care of community-dwelling patients in all countries. A one-point decrease in DAD resulted in a 1.4% increase in costs of care in Spain, United Kingdom, and the United States on average, and a 2% increase in Sweden. This translated into a 45% increase from a standard deviation decrease in DAD on average. NPI-severity and Mini-Mental State Examination were also significant predictors but with lesser effect. Although mean costs of care differed across countries, the important predictors were the same.
CONCLUSION: ADL-ability is the most important predictor of societal costs of care in community dwellings irrespective of country and should therefore be central in the economic evaluation of Alzheimer's disease therapies.