COHORT AND RACE DIFFERENCES IN FACTORS ASSOCIATED WITH ATTRITION IN LONGITUDINAL STUDIES OF ALZHEIMER’S DISEASE

Abstract

Across the US, longitudinal Alzheimer's disease (AD) studies will enroll approximately 70,000 subjects. Few studies have systematically examined the retention of these high-value participants. ADNI recently reported 50% attrition for longitudinal CSF collection at 12 months and 71% attrition by 48 months. More information is needed about the cohorts most likely to withdraw and the factors associated with attrition in order to develop retention programs. The Wisconsin Alzheimer's Disease Research Center (ADRC) enrolls participants with AD, mild cognitive impairment (MCI), Older Controls and middle-aged individuals with/without a parental history of AD. We examined reasons for attrition in these five longitudinal cohorts. Reasons for attrition from the Wisconsin ADRC Clinical Core were recorded and tabulated by cohort, race (African American (AA) vs All Others) and study visit. Cumulative attrition rates were computed by cohort, study visit, race/ethnicity and participation in imaging and CSF biomarker studies. Over 8 years 109 of 787 participants withdrew from the Clinical Core. Cumulative non-mortality attrition was 14%, attrition was significantly higher for AA (23%) than for non AA samples (12%). The AD cohort sustained the greatest loss (35%) followed by MCI (30%) and Older Controls (14%), attrition was lowest in middle-aged parental history positive and negative cohorts 11% and 2% respectively. The majority of participants (51%) withdrew after their baseline visit. Fifty-four percent completed at least 1 MRI and 30% completed at least 1 lumbar puncture (LP). “No longer interested in research” was the most common reason cited (33%) followed by “Loss to follow-up” (28%), Travel (16%) and Time (8%) constraints. Older Controls were more likely to cite travel constraints and loss of a study partner as factors than other groups. Retention is a significant issue in AD research as trials move toward earlier intervention in non-demented individuals. Attrition substantially increases the cost of longitudinal studies and clinical trials. Our findings support the need for more comprehensive evaluation of participant attrition, and development of both general and cohort specific retention strategies. Active engagement of participants after baseline visits and more effective communication of contributions of study participants to scientific progress is warranted.