Alzheimer's disease: the strength of association of costs with different measures of disease severity.

Objective: To identify Alzheimer's disease (AD) severity measures for use in cost-effectiveness models that effectively capture the impact of AD on costs.

Methods: A review of the literature and data abstraction from papers that present 1) mean AD costs (direct, indirect, or total) by disease severity, defined using measure of cognition, functional status, and behavior; and/or 2) the results of regression analyses that estimate the strength of the association between AD costs and disease severity.

Results: All papers reviewed showed that mean total costs increase with disease severity regardless of severity-measurement method. The relative difference in mean total costs between patients with severe disease compared to those with moderate disease, or moderate disease compared to mild disease, was fairly consistent across studies, suggesting that any of the disease-severity measures may be used to broadly categorize patients by cost. However, when regression analysis included multiple disease-severity measures, independent associations with costs were noted for the different measures. Cognitive and functional status measures were consistently associated with direct costs, whereas functional status and behavioral measures were consistently associated with indirect costs and caregiver hours.

Conclusions: Either multidimensional disease-severity measures, or a single disease-severity measure, that capture the impact of cognition, functional status, and behavior on costs are needed for cost-effectiveness models.