Health State Values for Use in the Economic Evaluation of Treatments for Alzheimer's Disease

Alzheimer's disease (AD) is a chronic, progressive, neurodegenerative disease that places a heavy burden on people with the condition, their families and carers, health care systems and society in general. Health-related quality of life (HR-QOL) in patients deteriorates as the cognitive, behavioural and functional symptoms of AD develop. The human and financial cost of AD is forecast to grow rapidly as populations age, and those responsible for planning and financing health care face the challenge of allocating increasingly scarce resources against current and future interventions targeted towards AD. These include calls for early detection and diagnosis, preventative strategies, new medications, residential care, supportive care, and meeting the needs of carers as well as patients. Health care funders in many health systems now require a demonstration of the value of new interventions through a comparison of benefits in terms of improvements in HR-QOL and costs relative to those of competing or existing practices. Changes in HR-QOL provide the basis for the calculation of the quality-adjusted life-year (QALY), a key outcome used in economic evaluations to compare treatments within and between different disease conditions. The objective of this systematic review was to provide a summary of the published health state values (utilities) for AD patients and their carers that are currently available to estimate QALYs for use in health economic evaluations of interventions in AD. The health care literature was searched for articles published in English between 2000 and 2011, using keywords and variants including 'quality-adjusted life years', 'health state indicators', 'health utilities' and the specific names of generic measures of HR-QOL and health state valuation techniques. Databases searched included MEDLINE, EMBASE, NHS EED, PsycINFO and ISI Web of Science. This review identified 12 studies that reported utility values associated with health states in AD. Values for AD health states categorized according to cognitive impairment (where 1 = perfect health and 0 = dead) ranged from mild AD (0.52-0.73) to moderate AD (0.30-0.53) to severe AD (0.12-0.49). Utility values were almost all based on two generic measures of HR-QOL: the EQ-5D and Health Utility Index mark 2/3 (HUI2/3). There were no health state values estimated from condition- or disease-specific measures of HR-QOL. The review also identified 18 published cost-utility analyses (CUAs) of treatments for AD. The CUAs incorporated results from only three of the identified health state valuation studies. Twelve CUAs relied on the same study for health state values. We conclude that the literature on health state values in AD is limited and overly reliant on a single symptom (cognition) to describe disease progression. Other approaches to characterizing disease progression in AD based on multiple outcomes or dependency may be better predictors of costs and utilities in economic evaluations. Patient and proxy ratings were poorly correlated, particularly in patients with more advanced AD. However, proxy ratings displayed the validity and reliability across the entire range of AD severity needed to detect long-term changes relevant to economic evaluation. Further longitudinal research of patient and carer HR-QOL based on multidimensional measures of outcome and utilities is needed.