COST: Cognitive State Test, a brief screening battery for Alzheimer disease in illiterate and literate patients

The aim was to develop a brief screening battery, Cognitive State Test (COST), for detecting the presence of dementia in both illiterate and literate patients and to assess its validity and reliability.

COST is a cognitive screening tool that consists of almost all cognitive domains. It takes 5-7 minutes to administer, and has a maximum score of 30. Data were obtained from 114 healthy volunteers and 74 Alzheimer dementia (AD) patients. Subjects' age divided into two groups: A1: <65 years; and A2: ≥65 years and their education level divided into three groups: E1: illiterate; E2: 1-5 years; and E3: ≥6 years. For assessing concurrent validity, total COST score was compared to the Clinical Dementia Rating (CDR), the Mini Mental State Examination (MMSE), the Montreal Cognitive Assessment (MoCA), and Basic Activities of Daily Living (BADL). Sensitivity and specificity were determined through a discriminant analysis using the Receiver Operating Characteristic (ROC) curves. Internal consistency was measured using Cronbach's coefficient α.

For normal and AD subjects, mean age was 64.9±9.8 years (50 women and 64 men) and 67.2±13.2 years (55 women and 19 men), respectively. Schooling ranged from 0-15 years (mean 5.7±4.2 and 3.3±3.8 years, respectively), and 21 and 37 subjects were illiterate, respectively. The COST significantly and positively correlated with MMSE and MoCA, and significantly and inversely correlated with CDR, the Geriatric Depression Scale (GDS), and BADL. In the E1, E2, and E3 education groups, the optimal cut-off points of COST chosen for diagnosis of AD were 23/24 (sensitivity: 81%, specificity: 99%), 24/25 (sensitivity: 75%, specificity: 86%), and 26/27 (sensitivity: 77%, specificity: 84%), respectively. When illiterate and literate subjects were then pooled, the optimal cut-off score of COST was 24/25, which yielded a sensitivity of 81% and a specificity of 87%. Reliability of the COST was good (0.86).

The COST is a valid and reliable screening battery for detection of dementia both in the illiterate and the literate Alzheimer patients.